Abstract:
An object is to provide a light emitting element using an inorganic compound as a light emitting material, which has ever-higher luminous efficiency and can be driven with low voltage. The chance of excitation of light emitting centers (atoms) in a light emitting layer is increased to enhance luminous efficiency by providing a carrier supply layer in order to increase the number of carries in the light emitting layer of a light emitting element using an inorganic compound, and drive voltage of the light emitting element or a light emitting device is reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light emitting element using electroluminescence. The present invention also relates to a light emitting device and an electronic device each including the light emitting element. 
     2. Description of the Related Art 
     In recent years, light emitting elements using electroluminescence have been actively researched and developed. In a basic structure of the light emitting element, a light emitting substance is interposed between a pair of electrodes. Light emission from the light emitting substance can be obtained by voltage application between the electrodes. 
     Such a light emitting element is of a self-light emitting type; therefore, it has advantages over a liquid crystal display in wide viewing angle, excellent visibility, high response speed, and capability of reduction in thickness and weight. 
     Light emitting elements can be divided into two groups: an organic light emitting element using an organic compound as a light emitting substance, and an inorganic light emitting element using an inorganic compound. 
     Note that these light emitting elements differ from each other in not only light emitting substance but also light emitting mechanism and characteristic. 
     Of them, the inorganic light emitting element has a double insulating structure which includes a light emitting layer  1503  interposed between insulating films (a first insulating film  1502  and a second insulating film  1504 ), between a pair of electrodes (a first electrode  1501  and a second electrode  1505 ), and provides light emission by application of an alternating voltage between both electrodes (the first electrode  1501  and the second electrode  1505 ) from respective power sources (a first power source  1506  and a second power source  1507 ), as shown in  FIG. 15 . 
     However, although the inorganic light emitting element has more excellent material reliability than the organic light emitting element, sufficient luminance and the like have not been obtained and various researches have been carried out (for example, see Reference 1: Japanese Published Patent Application No. 2001-250691). 
     Further, the inorganic light emitting element requires application of a voltage of several-hundred volts to the light emitting element due to its light emitting mechanism which provides light emission through collisional excitation of a light emitting center by electrons accelerated with high electric field. It is important to reduce its drive voltage in order to apply the inorganic light emitting element to a display panel or the like. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a light emitting element using an inorganic compound as a light emitting material, which has ever-higher luminous efficiency and which can be driven with low voltage. 
     A conventional light emitting element using an inorganic compound has a light emitting mechanism by which light is emitted as energy when inner-shell electrons of light emitting centers (atoms) excited by collision of carriers in a light emitting layer returns to a ground state. Therefore, one reason for high drive voltage of the light emitting element is that the number of carriers for exciting light emitting centers is insufficient. 
     On the other hand, a feature of the present invention is to increase the chance of excitation of light emitting centers (atoms) in a light emitting layer to enhance luminous efficiency by providing a carrier supply layer in order to increase the number of carriers in the light emitting layer of a light emitting element using an inorganic compound, and to reduce drive voltage of the light emitting element or a light emitting device. 
     In specific, a light emitting device of the present invention includes a first electrode; a first insulating film formed over the first electrode; a light emitting layer formed over the first insulating film; a second insulating film formed over the light emitting layer; a second electrode formed over the second insulating film; and a carrier supply layer interposed between the first and second insulating films. The light emitting layer includes at least a base material and an additive material, and the carrier supply layer comprises a semiconductor material which includes at least one of an n-type impurity element and a p-type impurity element. 
     Note that the present invention includes, in its scope, a structure with a plurality of carrier supply layers. Another light emitting device according to the present invention includes a first electrode; a first insulating film formed over the first electrode; a light emitting layer formed over the first insulating film; a second insulating film formed over the light emitting layer; a second electrode formed over the second insulating film; and a plurality of carrier supply layers interposed between the first and second insulating films. 
     In addition, the present invention also includes, in its scope, a structure in which the light emitting layer is partially in contact with the carrier supply layer as well as the above-mentioned structures. 
     In each of the above structures, the base material is one or more of the following materials: a Group 2-Group 16 compound, a Group 12-Group 16 compound, a Group 13-Group 15 compound, a Group 2-Group 13-Group 16 compound, a Group 14 compound, and rare-earth sulfide. More specifically, the base material is one or more of the following materials: calcium sulfide, strontium sulfide, barium sulfide, zinc sulfide, cadmium sulfide, zinc oxide, gallium nitride, strontium gallium sulfide, magnesium zinc oxide, silicon carbide, and yttrium sulfide. 
     In each of the above structures, the additive material is one or more of transition metal elements and rare-earth elements. More specifically, it is one or more of the following materials: cerium, praseodymium, samarium, europium, terbium, thulium, chromium, iron, cobalt, nickel, copper, silver, gold, platinum, and manganese. 
     In each of the above structures, the carrier supply layer comprises one of the following materials: zinc sulfide to which indium is added, zinc oxide to which aluminum or gallium is added, gallium nitride to which silicon is added, zinc oxide to which nitrogen or phosphorus is added, and gallium nitride to which zinc is added. 
     Note that the light emitting device in this specification includes, in its category, an image display device, a light emitting device, and a light source (including a lighting system). Further, the light emitting device includes all of the following modules: a module in which a connector such as an FPC (Flexible Printed Circuit), a TAB (Tape Automated Bonding) tape, or a TCP (Tape Carrier Package) is attached to a panel provided with the light emitting elements described in this specification; a module having a TAB tape or a TCP provided with a printed wiring board at the end thereof; and a module having an IC (Integrated Circuit) directly mounted on a light emitting device by a COG (Chip On Glass) method. 
     The present invention includes, in its scope, an electronic device using the light emitting device of the present invention in a display portion. 
     A light emitting element having not only high luminous efficiency and low drive voltage but also high resistance to deterioration can be provided by carrying out the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a light emitting element of the present invention. 
         FIGS. 2A and 2B  are diagrams illustrating a light emitting element of the present invention. 
         FIG. 3  is a diagram illustrating a light emitting element of the present invention. 
         FIGS. 4A and 4B  are diagrams each illustrating a light emitting element of the present invention. 
         FIGS. 5A to 5D  are diagrams illustrating carrier movement in a light emitting element of the present invention. 
         FIGS. 6A and 6B  are diagrams illustrating circuit structures of an active-matrix light emitting device of the present invention. 
         FIGS. 7A and 7B  are diagrams illustrating a pixel portion of an active-matrix light emitting device of the present invention. 
         FIGS. 8A to 8E  are diagrams illustrating a method for manufacturing an active-matrix light emitting device of the present invention. 
         FIGS. 9A to 9C  are diagrams illustrating a method for manufacturing an active-matrix light emitting device of the present invention. 
         FIGS. 10A to 10C  are diagrams illustrating a method for manufacturing an active-matrix light emitting device of the present invention. 
         FIGS. 11A and 11B  are diagrams illustrating a method for manufacturing an active-matrix light emitting device of the present invention. 
         FIGS. 12A and 12B  are diagrams illustrating an active-matrix light emitting device of the present invention. 
         FIGS. 13A to 13D  are diagrams illustrating a passive-matrix light emitting device of the present invention. 
         FIGS. 14A to 14E  are diagrams illustrating electronic devices. 
         FIG. 15  is a diagram illustrating a conventional inorganic light emitting element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment modes of the present invention are hereinafter described in detail with reference to the drawings and the like. Note that the present invention can be embodied in many different modes, and it is easily understood by the skilled person that the mode and the detail of the present invention can be variously changed without deviating from the spirit and the scope thereof. Therefore, the present invention is not interpreted as being limited to the description of the following embodiment modes. 
     Embodiment Mode 1 
     This embodiment mode describes a light emitting element of the present invention. Note that it is important in the present invention to sufficiently supply carriers to a light emitting layer in order to increase luminous efficiency of the light emitting element. 
     The light emitting element of the present invention has a structure shown in  FIG. 1 . In other words, it has a structure in which a first insulating film  102  is formed of an insulating material over a first electrode  101  made of a conductive material; a plurality of carrier supply layers  103  is partly and separately formed over the first insulating film  102 ; a light emitting layer  104  is formed so as to be partly in contact with the carrier supply layers  103 ; a second insulating film  105  is formed of an insulating material over the light emitting layer  104 ; and a second electrode  106  is formed of a conductive material over the second insulating film  105 . 
     In the present invention, the light emitting layer  104  is formed of a base material that is a semiconductor and an additive material that is a light emitting center. The carrier supply layers  103  are formed by addition of a p-type or n-type impurity element to a semiconductor material. Specific examples of the base material, the additive material, and the p-type or n-type impurity element will be given later in this embodiment mode. 
     Therefore, in the element structure of the light emitting element of the present invention, the carrier supply layers  103  and the light emitting layer  104  which is formed to be partly in contact with the carrier supply layers  103  are interposed between the first insulating film  102  and the second insulating film  105 , and they are further interposed between the first electrode  101  and the second electrode  106  with the first insulating film  102  and the second insulating film  105  interposed therebetween. 
     When an alternating voltage (of, for example, 10 V to 100 V) is applied between both of the electrodes (the first electrode  101  and the second electrode  106 ), carriers (electrons) are supplied from the carrier supply layers  103  to the light emitting layer  104 . Note that since the carrier concentration (electron concentration) of each carrier supply layer  103  when voltage is applied is much higher than that of the light emitting layer  104 , carriers can be efficiently supplied to the light emitting layer  104  and drive voltage can be reduced. 
     Next, a carrier supply mechanism of the light emitting element is described with reference to band diagrams of  FIGS. 2A and 2B . Note that each of  FIGS. 2A and 2B  shows, as an example, a case of a light emitting element which includes a light emitting layer  201  formed using zinc sulfide (ZnS) as a base material and manganese (Mn) as an additive material and a carrier supply layer  202  formed using indium (In) as an n-type impurity element in a semiconductor material. 
       FIG. 2A  is a band diagram showing a state in which voltage is not applied to either of the electrodes of the light emitting element (a thermal equilibrium state). In  FIG. 2A , carriers  203  cannot be supplied from the carrier supply layer  202  to the light emitting layer  201  because there is a large difference in work function (hereinafter referred to as a diffusion potential) between substances included in the light emitting layer  201  and the carrier supply layer  202 . 
     However, the diffusion potential becomes small as shown in  FIG. 2B  by application of negative voltage to a first electrode (or positive voltage to a second electrode); thus, the carriers  203  can be supplied from the carrier supply layer  202  to the light emitting layer  201 . 
     Therefore, drive voltage can be reduced because carriers can be efficiently supplied to a light emitting layer when a carrier supply layer is formed so as to be partly in contact with the light emitting layer as in the present invention. 
     Each of the first electrode  101  and the second electrode  106  of the light emitting element of the present invention can be formed using a conductive film including a semiconductor such as Si or Ge; a single-layer conductive film of a metal element such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, or Nd; a stacked conductive film of a plurality of the above metal elements; a conductive film made of an alloy which includes the metal element as its main component (such as an aluminum-titanium alloy film); a conductive film made of metal nitride using the metal element; or the like. 
     Alternatively, it may be formed using a conductive film of indium tin oxide (ITO), indium zinc oxide (IZO) formed using a target in which indium oxide containing silicon oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, indium tin oxide containing silicon oxide as a component (ITSO), or the like. 
     Note that the thickness of each of the first electrode  101  and the second electrode  106  is preferably 50 nm to 400 nm, more preferably 100 nm to 250 nm. 
     Each of the first insulating film  102  and the second insulating film  105  can be formed to have a single-layer or stacked structure using an insulating film containing silicon such as a silicon oxide (for example, SiO 2 ) film, a silicon nitride (for example, Si 3 N 4 ) film, a silicon nitride oxide film, or a silicon oxynitride film, or an insulating film of metal oxide (for example, Al 2 O 3  or BaTiO 3 ) or the like. Note that the thickness of each of the first insulating film  102  and the second insulating film  105  is 10 nm to 250 nm, preferably 100 nm to 200 nm. 
     The light emitting layer  104  is formed of a base material that is a semiconductor and an additive material that is a light emitting center. Note that the base material can be any of the following materials: a compound including a Group 2 element and Group 16 element of the periodic table (hereinafter referred to as a Group 2-Group 16 compound), a compound including a Group 12 element and a Group 16 element (hereinafter referred to as a Group 12-Group 16 compound), a compound including a Group 13 element and a Group 15 element (hereinafter referred to as a Group 13-Group 15 compound), a compound including a Group 2 (or Group 12 or rare-earth) element, a Group 13 element, and a Group 16 element (hereinafter referred to as a Group 2-Group 13-Group 16 compound), a compound including a plurality of Group 14 elements (hereinafter referred to as a Group 14 compound), a compound including a rare-earth element and sulfur (S) (hereinafter referred to as rare-earth sulfide), a combination thereof, and the like. 
     Note that examples of the Group 2-Group 16 compound are as follows: calcium sulfide (CaS), strontium sulfide (SrS), barium sulfide (BaS), and the like. Specific examples of the Group 12-Group 16 compound are as follows: zinc sulfide (ZnS), cadmium sulfide (CdS), zinc oxide (ZnO), and the like; the Group 13-Group 15 compound, gallium nitride (GaN) and the like; the Group 2-Group 13-Group 16 compound, strontium gallium sulfide (SrGa 2 S 4 ), magnesium zinc oxide (Mg x Zn 1-x O), and the like; the Group 14 compound, silicon carbide (SiC) and the like; and the rare-earth sulfide, yttrium sulfide (Y 2 S 3 ) and the like. 
     The additive material can be a transition metal, a rare-earth element, or the like. Note that specific examples of the additive material are as follows: cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), terbium (Tb), thulium (Tm), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), gold (Au), platinum (Pt), manganese (Mn), and the like. 
     Further, specific examples of a combination of the base material and the additive material (base material:additive material) are as follows: ZnS:Mn, CdSSe:Mn, ZnS:TbOF, ZnS:Tb, SrS:Ce, SrGa 2 S 4 :Ce, and the like. 
     Note that the composition ratio of the above-mentioned compound does not take an exact value and has a certain degree of solid solubility limit (or a composition range) for each element. Therefore, it is acceptable in the present invention as long as the composition ratio is in that range. 
     The carrier supply layers  103  can be formed using a semiconductor material (including the above-mentioned semiconductor serving as the base material) which includes an n-type or p-type impurity element. 
     The n-type impurity element can be as follows: indium (In), aluminum (Al), gallium (Ga), silicon (Si), or the like. The p-type impurity element can be as follows: nitrogen (N), phosphorus (P), zinc (Zn), or the like. 
     Note that specific examples of a material which is used for the carrier supply layers  103  and is a combination of a semiconductor material and the n-type or p-type impurity element added to the semiconductor material are as follows: n-type ZnS in which an n-type impurity element. In, is added to a semiconductor material, ZnS; n-type ZnO in which an n-type impurity element, Al or Ga, is added to a semiconductor material, ZnO; n-type GaN in which an n-type impurity element, Si, is added to a semiconductor material, GaN; p-type ZnO in which a p-type impurity element, N or P, is added to a semiconductor material, ZnO; p-type GaN in which a p-type impurity element, Zn, is added to a semiconductor material, GaN; and the like. 
     In the light emitting element of the present invention having the above-described structure, the efficiency of carrier supply to the light emitting layer can be increased due to the carrier supply layers provided so as to be partly in contact with the light emitting layer, so that drive voltage thereof can be reduced. 
     Embodiment Mode 2 
     This embodiment mode describes the principle of carrier supply in a case of driving the light emitting element of the present invention. 
       FIG. 3  shows a structure of the light emitting element of the present invention. The light emitting element of the present invention has a structure in which a first insulating film  302  is formed of an insulating material over a first electrode  301  made of a conductive material; a plurality of carrier supply layers  303  is partly and separately formed over the first insulating film  302 ; a light emitting layer  304  is formed over the carrier supply layers  303 ; a second insulating film  305  is formed of an insulating material over the light emitting layer  304 ; and a second electrode  306  is formed of a conductive material over the second insulating film  305 . 
     Note that the first electrode  301  is electrically connected to a first power source  307 , and a constant voltage (reference voltage) is applied from the first power source  307  to the first electrode  301  as shown in  FIG. 4A . 
     On the other hand, the second electrode  306  is electrically connected to a second power source  308 , and voltages having positive and negative polarities with respect to the reference voltage are alternately applied from the second power source  308  to the second electrode  306  as time (t) (the horizontal axis of  FIG. 4B ) passes, as shown in  FIG. 4B . 
     Note that the above-mentioned voltage having positive polarity refers to a voltage which is higher than the reference voltage applied from the first power source  307  to the first electrode  301 , and the voltage having negative polarity refers to a voltage which is lower than the reference voltage applied from the first power source  307  to the first electrode  301 . 
     Next, the states of carriers in the light emitting layer of the light emitting element of the present invention are described with reference to model diagrams of  FIGS. 5A to 5D . Note that the same reference numerals are used in  FIG. 3  and  FIGS. 5A to 5D  for convenience of explanation. 
     First, when the voltage having positive polarity is applied to the second electrode  306  (t=t 1  in  FIG. 4B ), carriers are supplied from the carrier supply layers  303  to an upper interface of the light emitting layer  304  with the second insulating film  305  as shown in  FIG. 5A . 
     Next, when the voltage having negative polarity is applied to the second electrode  306  (t=t 2  in  FIG. 4B ), the carriers are accelerated, as indicated by arrows in  FIG. 5B , by an electric field generated by the voltage having negative polarity which is applied to the second electrode  306 , and the carriers collide with atoms of the additive material included in the light emitting layer  304 , thereby exciting electrons in the atoms of the additive material. The excited electrons are immediately released to a ground state, and energy at that time is emitted as light. 
     Further, in a state where the voltage having negative polarity is applied to the second electrode  306  (t=t 3  in  FIG. 4B ), the carriers are supplied from the carrier supply layers  303  to a lower interface of the light emitting layer  304  with the first insulating film  302 . 
     When the voltage having positive polarity is applied to the second electrode  306  again (t=t 4  in  FIG. 4B ), the carriers present near the interface between the light emitting layer  304  and the first insulating film  302  are accelerated by an electric field as indicated by arrows in  FIG. 5D , and the carriers collide with atoms of the additive material included in the light emitting layer  304 , thereby exciting electrons in the atoms of the additive material. 
     Thus, alternate application of a voltage having positive polarity and a voltage having negative polarity to the second electrode  306  can cause light emission in the light emitting layer  304  of the light emitting element. 
     In the light emitting element of this embodiment mode, the efficiency of carrier supply to the light emitting layer can be increased due to the carrier supply layers provided so as to be partly in contact with the light emitting layer, so that drive voltage thereof can be reduced. 
     Embodiment Mode 3 
     This embodiment mode describes an active-matrix light emitting device in which each of pixels included in a pixel portion includes a thin film transistor (TFT) and the light emitting element of the present invention. 
     Note that the active-matrix light emitting device can have such a circuit structure as shown in either  FIG. 6A  or  6 B. 
       FIG. 6A  shows a structure in which each pixel includes a single light emitting element and a single TFT functioning as a switch of the light emitting element. Therefore, the TFT shown in  FIG. 6A  is referred to as a switching TFT ( 603 ). 
     A gate electrode of the switching TFT  603  is connected to a gate line (Gj)  602 . One terminal connected to a channel formation region of the switching TFT  603  is electrically connected to a source line (Si)  601 , and the other terminal is electrically connected to one electrode of a light emitting element  604 . Note that the other electrode of the light emitting element  604  is electrically connected to a counter power source  605  maintaining a constant voltage (reference voltage). 
     A signal for turning on or off the switching TFT  603  (DC voltage V gate ) is inputted through the gate line (Gj)  602 . A signal for driving the light emitting element  604  (AC voltage V sig ) is inputted through the source line (Si)  601 ; here, a voltage higher than the reference voltage (voltage having positive polarity) and a voltage lower than the reference voltage (voltage having negative polarity) are alternately applied periodically. 
     Note that a gray scale can be expressed by changing the amplitude of V sig . 
       FIG. 6B  shows a structure in which each pixel includes a single light emitting element and two TFTs. Note that the TFTs here are of two kinds: a driving TFT  614  functioning to drive a light emitting element  615  and a switching TFT  613  functioning as a switch of the driving TFT  614 . 
     A gate electrode of the switching TFT  613  is connected to a gate line (Gj)  612 . One terminal connected to a channel formation region of the switching TFT  613  is electrically connected to a source line (Si)  611 , and the other terminal is electrically connected to a gate electrode of the driving TFT  614 . 
     One terminal connected to a channel formation region of the driving TFT  614  is electrically connected to a current supply line (Vi)  617 , and the other terminal is electrically connected to one electrode of the light emitting element  615 . Note that the other electrode of the light emitting element  615  is electrically connected to a counter power source  616  maintaining a constant voltage (reference voltage). 
     A signal for turning on or off the switching TFT  613  (DC voltage V gate ) is inputted through the gate line (Gj)  612 , and a signal for turning on or off the driving TFT  614  (DC voltage V sig ) is inputted through the source line (Si)  611 . An alternating voltage for driving the light emitting element  615  is inputted through the current supply line (Vi)  617 ; here, a voltage higher than the reference voltage (voltage having positive polarity) and a voltage lower than the reference voltage (voltage having negative polarity) are alternately applied periodically. 
     Note that a gray scale can be expressed by changing the amplitude of V sig . 
     Next, a detailed structure of a pixel portion of an active-matrix light emitting device having the circuit structure shown in  FIG. 6B  is described with reference to  FIGS. 7A and 7B . Note that  FIG. 7A  is a top view showing a driving portion of a pixel, and  FIG. 7B  shows a cross-sectional view taken along a line A-A′ in  FIG. 7A . 
       FIG. 7A  shows a driving portion of a pixel, which includes a gate line  702 , a source line  709 , and a current supply line  708 . Note that each pixel includes two TFTs, a switching TFT  717  and a driving TFT  718 . A part of the gate line  702  serves as a gate electrode of the switching TFT  717 , and a part of a semiconductor film  705  which also functions as a channel formation region of the switching TFT  717  is electrically connected to the source line  709 . 
     Another part of the semiconductor film  705  which also functions as the channel formation region of the switching TFT  717  is electrically connected to a gate electrode  703  of the driving TFT  718 . Note that a part of a semiconductor film  706  which also functions as a channel formation region of the driving TFT  718  is electrically connected to the current supply line  708 , and another part of the semiconductor film  706  is electrically connected to one electrode (here, referred to as a first electrode  711 ) of a light emitting element, which functions as a pixel electrode. 
     Next, the cross-sectional structure shown in  FIG. 7B  is described. The gate electrodes  702  and  703  are formed over a substrate  701  by patterning a conductive film made of a conductive material. Note that the gate electrode  702  is a part of the gate line. 
     A first insulating film  704  is formed of an insulating material over the gate electrodes  702  and  703 , respective parts of which function as gate insulating films of the switching TFT  717  and the driving TFT  718 . 
     The semiconductor films  705  and  706  are formed over the first insulating film  704 . Note that an inorganic semiconductor material which includes as its main component silicon, silicon germanium (SiGe), gallium arsenide (GaAs), zinc oxide (ZnO), or the like can be used for the semiconductor films  705  and  706 . Alternatively, an organic semiconductor material which includes pentacene, oligothiophene, or the like as its main component can be used for the semiconductor films  705  and  706 . 
     Note that the semiconductor films  705  and  706  are patterned into a desired shape as shown in  FIGS. 7A and 7B  and are electrically connected to other wirings, electrodes, and the like. 
     A second insulating film  707  is formed of an insulating material over the semiconductor films  705  and  706 . Note that the second insulating film  707  functions as a so-called first interlayer insulating film. 
     A wiring is formed over the second insulating film  707  by patterning a conductive film made of a conductive material. Note that a wiring  709  functioning as the source line is formed to be electrically connected to the semiconductor film  705  previously formed, and although not shown in  FIG. 7B , a wiring  708  functioning as the current supply line is formed to be electrically connected to one terminal of the driving TFT. 
     A third insulating film  710  is formed of an insulating material over these wirings  708  and  709 . Note that the third insulating film  710  functions as a so-called second interlayer insulating film. 
     The first electrode  711  functioning as one electrode of the light emitting element is formed over the third insulating film  710 . Note that the first electrode  711  is electrically connected to the semiconductor film  706  with the second insulating film  707  and the third insulating film  710  interposed therebetween, and is patterned into a desired shape so as to serve as the pixel electrode that constitutes a part of one pixel. 
     A fourth insulating film  712  is formed of an insulating material over the first electrode  711 . Note that the fourth insulating film  712  functions as one of insulating films that constitute a part of a double insulating structure in the light emitting element. 
     A carrier supply layer  713  is formed over the fourth insulating film  712 . Note that the carrier supply layer  713  can be formed using a material similar to that described in Embodiment Mode 1. 
     A light emitting layer  714  is formed over the carrier supply layer  713 . Note that the light emitting layer  714  can be formed using the base material and the additive material described in Embodiment Mode 1. 
     A fifth insulating film  715  is formed of an insulating material over the light emitting layer  714 . Note that the fifth insulating film  715  functions as the other of the insulating films that constitute a part of the double insulating structure in the light emitting element. 
     A second electrode  716  functioning as the other electrode of the light emitting element is formed over the fifth insulating film  715 . 
     As described above, in the active-matrix light emitting device described in this embodiment mode, the efficiency of carrier supply to the light emitting layer can be increased due to the carrier supply layer provided so as to be partly in contact with the light emitting layer, so that drive voltage thereof can be reduced. 
     Embodiment Mode 4 
     This embodiment mode describes a method for manufacturing an active-matrix light emitting device in which each of pixels included in a pixel portion includes two thin film transistors (TFTs) and the light emitting element of the present invention. 
     As shown in  FIG. 8A , a first conductive film  902  is formed over a substrate  901 . The first conductive film  902  is formed by a film formation method such as a sputtering method, a PVD method, a CVD method, a droplet discharge method, an ink-jet method, or a printing method, using a conductive film including a semiconductor such as Si or Ge; a single-layer conductive film of a metal element such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, or Nd; a stacked conductive film of a combination of a plurality of the above metal elements; a conductive film made of an alloy which includes the metal element as its main component (such as an aluminum-titanium alloy film); a conductive film made of a metal nitride using the metal element; or the like. Alternatively, it may be formed using a conductive film of indium tin oxide (ITO), indium zinc oxide (IZO) formed using a target in which indium oxide containing silicon oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, indium tin oxide containing silicon oxide as a component (ITSO), or the like. 
     Note that the conductive film in this specification refers to a film with a resistivity of 1×10 −3  Ωcm or less. 
     The thickness of the first conductive film  902  is preferably 50 nm to 500 nm, more preferably 150 nm to 300 nm. 
     The substrate  901  can be any of the following: a glass substrate, a quartz substrate, a substrate formed of an insulating substance like ceramic such as alumina, a plastic substrate, a silicon wafer, a metal plate, paper, and the like. 
     Next, gate electrodes  903  and  904  are formed by patterning the first conductive film  902  ( FIG. 8B ). When the first conductive film  902  is formed using a film formation method such as a sputtering method or a CVD method, a mask is formed over the conductive film by a droplet discharge method, a photolithography step, light exposure and development of a photosensitive material using a laser-beam direct drawing apparatus, or the like, and the conductive film is patterned into a desired shape using the mask. 
     Next, a first insulating film  905  is formed. The first insulating film  905  can be formed by a film formation method such as a CVD method or a sputtering method, using a single-layer film of an insulating film containing silicon such as a silicon oxide (for example, SiO 2 ) film, a silicon nitride (for example, Si 3 N 4 ) film, a silicon oxynitride film, or a silicon nitride oxide film or an insulating film of metal oxide (for example, Al 2 O 3  or BaTiO 3 ) or the like, or a stacked film formed by stacking the single-layer films. Note that since the first insulating film  905  functions as a gate insulating film, the thickness thereof is preferably 50 nm to 200 nm, more preferably 100 nm to 150 nm. 
     Next, as shown in  FIG. 8C , first masks  906   a  and  906   b  are formed in a desired position over the first insulating film  905  by, for example, a droplet discharge method, a photolithography step, light exposure and development of a photosensitive material using a laser-beam direct drawing apparatus, or the like. Then, an opening is formed in a part of the first insulating film  905  so as to reach the gate electrode  904 . 
     After the first masks  906   a  and  906   b  are removed, a first semiconductor film  907  is formed over the first insulating film  905 . The first semiconductor film  907  can be formed by a film formation method such as a CVD method or a sputtering method, using an inorganic semiconductor material such as silicon, silicon germanium (SiGe), gallium arsenide (GaAs), zinc oxide (ZnO), or the like or an organic semiconductor material such as pentacene or oligothiophene. 
     Note that the first semiconductor film  907  may include an acceptor element or a donor element such as phosphorus, arsenic, or boron in addition to the above-mentioned main component. The thickness of the first semiconductor film  907  is 40 nm to 250 nm, preferably 50 nm to 150 nm. 
     Next, as shown in  FIG. 8D , second masks  908   a  and  908   b  are formed in a desired position over the first semiconductor film  907 , and the first semiconductor film  907  is patterned into a desired shape by etching with the use of the second masks  908   a  and  908   b , thereby obtaining first semiconductor films  909  and  910  ( FIG. 8E ). 
     Next, a second insulating film  911  is formed. Note that the second insulating film  911  is formed by a film formation method such as a plasma CVD method or a sputtering method to have a single-layer or stacked structure using an insulating film such as a silicon oxide film, a silicon nitride film, a silicon nitride oxide film, or a silicon oxynitride film. Note that the thickness of the second insulating film  911  is 300 nm to 800 nm, preferably 400 nm to 600 nm. 
     Further, as shown in  FIG. 9A , third masks  912   a  and  912   b  are formed in a desired position over the second insulating film  911 , and an opening is formed in a part of the second insulating film  911  using the third masks  912   a  and  912   b  so as to reach the first semiconductor film  909 . Note that although not shown, another opening is also formed at this time so as to reach the first semiconductor film  910 . 
     After the third masks  912   a  and  912   b  are removed, a second conductive film  913  is formed over the second insulating film  911 . The second conductive film  913  can be formed using a film formation method such as a sputtering method, a PVD method, a CVD method, a droplet discharge method, an ink-jet method, or a printing method. Note that the thickness of the second conductive film  913  is preferably 100 nm to 700 nm, more preferably 150 nm to 300 nm. 
     The second conductive film  913  can be formed using a conductive film including a semiconductor such as Si or Ge; a single-layer conductive film of a metal element such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, or Nd; a stacked conductive film of a combination of a plurality of the above metal elements; a conductive film made of an alloy which includes the metal element as its main component (such as an aluminum-titanium alloy film); a conductive film made of metal nitride using the metal element; or the like. Alternatively, it may be formed using a conductive film of indium tin oxide (ITO), indium zinc oxide (IZO) formed using a target in which indium oxide containing silicon oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, indium tin oxide containing silicon oxide as a component (ITSO), or the like. Note that the above metal element in paste form may be used when using an ink-jet method. 
     Fourth masks  914   a  and  914   b  are formed over the second conductive film  913 , and a part of the second conductive film  913  is etched to form a desired shape. Of second conductive films  915  and  916  which are formed by patterning at this time, the second conductive film  915  functions as a current supply line and the second conductive film  916  functions as a source line. The second conductive film  916  is electrically connected to the first semiconductor film  909  as shown in  FIG. 9C . Note that the second conductive film  915  is also electrically connected to the first semiconductor film  910  through the opening previously formed although not shown. 
     Next, a third insulating film  917  is formed. The third insulating film  917  is formed by a film formation method such as a CVD method or a sputtering method to have a single-layer or stacked structure using an insulating film such as a silicon oxide film, a silicon nitride film, a silicon nitride oxide film, or a silicon oxynitride film. The thickness of the third insulating film  917  is 800 nm to 2000 nm, preferably 1000 nm to 1500 nm. 
     Further, as shown in  FIG. 9C , fifth masks  918   a  and  918   b  are formed in a desired position over the third insulating film  917 , and an opening is formed in a part of the third insulating film  917  using the fifth masks  918   a  and  918   b  so as to reach the first semiconductor film  910 . 
     After the fifth masks  918   a  and  918   b  are removed, a third conductive film  919  is formed over the third insulating film  917 . The third conductive film  919  can be formed using a film formation method such as a sputtering method, a PVD method, a CVD method, a droplet discharge method, an ink-jet method, or a printing method. Note that the thickness of the third conductive film  919  is preferably 50 nm to 400 nm, more preferably 100 nm to 250 nm. 
     The third conductive film  919  can be formed using a conductive film including a semiconductor such as Si or Ge; a single-layer conductive film of a metal element such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, or Nd; a stacked conductive film of a combination of a plurality of the above metal elements; a conductive film made of an alloy which includes the metal element as its main component (such as an aluminum-titanium alloy film); a conductive film made of metal nitride using the metal element; or the like. Alternatively, it may be formed using a conductive film of indium tin oxide (ITO), indium zinc oxide (IZO) formed using a target in which indium oxide containing silicon oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, indium tin oxide containing silicon oxide as a component (ITSO), or the like. Note that the above metal element in paste form may be used when using an ink-jet method. 
     The third conductive film  919  functions as one electrode of the light emitting element. Therefore, when it is required to have a function as an electrode through which light obtained in the light emitting layer of the light emitting element is extracted, a material with high transmittance (for example, 40% or higher) with respect to visible light is preferably selected from the above materials to form the third conductive film  919 . When the third conductive film  919  is formed as an electrode through which light does not need to be extracted, a material with low transmittance (for example, lower than 10%) with respect to visible light or a material with high reflectance (for example, 40% or higher) is preferably selected from the above materials to form the third conductive film  919 . 
     A sixth mask (not shown) is formed over the third conductive film  919 , and a part of the third conductive film  919  is etched to form a desired shape. The third conductive film  919  patterned here is one electrode of the light emitting element and functions as a pixel electrode. Note that the third conductive film  919  is electrically connected to the first semiconductor film  910  previously formed ( FIG. 10A ). 
     After the sixth mask (not shown) is removed, a fourth insulating film  920  which functions as one of insulating films of the light emitting element is formed over the patterned third conductive film  919  ( FIG. 10A ). Note that the fourth insulating film  920  is formed by a film formation method such as a CVD method or a sputtering method to have a single-layer or stacked structure using an insulating film containing silicon such as a silicon oxide (for example, SiO 2 ) film, a silicon nitride (for example, Si 3 N 4 ) film, a silicon nitride oxide film, or a silicon oxynitride film, or an insulating film of metal oxide (for example, Al 2 O 3  or BaTiO 3 ) or the like. Note that the thickness of the fourth insulating film  920  is 50 nm to 250 nm, preferably 100 nm to 200 nm. 
     Next, a second semiconductor film  921  is formed over the fourth insulating film  920 . Note that the second semiconductor film  921  includes an impurity which imparts n-type or p-type conductivity to the second semiconductor film. 
     The second semiconductor film  921  can be formed by a film formation method such as a CVD method or a sputtering method. Note that the thickness of the second semiconductor film  921  is 50 nm to 300 nm, preferably 100 nm to 200 nm. 
     The second semiconductor film  921  can be formed using a semiconductor material such as zinc sulfide (ZnS), gallium nitride (GaN), or zinc oxide (ZnO), another known semiconductor material, or the like which includes indium (In), aluminum (Al), gallium (Ga), silicon (Si), or the like as an n-type impurity element or nitrogen (N), phosphorus (P), zinc (Zn), or the like as a p-type impurity element. 
     Note that specific examples of the material used for the second semiconductor film  921  are as follows: n-type ZnS to which In or the like is added, n-type ZnO to which Al or Ga is added, n-type GaN to which Si is added, p-type ZnO to which N or P is added, p-type GaN to which Zn is added, and the like. 
     Seventh masks  922   a ,  922   b , and  922   c  are formed over the second semiconductor film  921  as shown in  FIG. 10B , and a part of the second semiconductor film  921  is etched to form a desired shape. Second semiconductor films  923   a ,  923   b , and  923   c  which are formed by patterning here function as carrier supply layers. 
     After the seventh masks  922   a ,  922   b , and  922   c  are removed, a light emitting layer  924  is formed over the second semiconductor film  923   a ,  923   b , and  923   c  formed by patterning. Note that the light emitting layer  924  includes a base material that is a semiconductor and an additive material that is a light emitting center. 
     The base material can be any of the following materials: a compound including a Group 2 element and a Group 16 element of the periodic table (hereinafter referred to as a Group 2-Group 16 compound), a compound including a Group 12 element and a Group 16 element (hereinafter referred to as a Group 12-Group 16 compound), a compound including a Group 13 element and a Group 15 element (hereinafter referred to as a Group 13-Group 15 compound), a compound including a Group 2 (or Group 12 or rare-earth) element, a Group 13 element, and a Group 16 element (hereinafter referred to as a Group 2-Group 13-Group 16 compound), a compound including a plurality of Group 14 elements (hereinafter referred to as a Group 14 compound), a compound including a rare-earth element and sulfur (S) (hereinafter referred to as rare-earth sulfide), a combination thereof, and the like. 
     Examples of the Group 2-Group 16 compound are as follows: calcium sulfide (CaS), strontium sulfide (SrS), barium sulfide (BaS), and the like. Examples of the Group 12-Group 16 compound are as follows: zinc sulfide (ZnS), cadmium sulfide (CdS), zinc oxide (ZnO), and the like; the Group 13-Group 15 compound, gallium nitride (GaN) and the like; the Group 2-Group 13-Group 16 compound, strontium gallium sulfide (SrGa 2 S 4 ), magnesium zinc oxide (MgZn 1-x O), and the like; the Group 14 compound, silicon carbide (SiC) and the like; and the rare-earth sulfide, yttrium sulfide (Y 2 S 3 ) and the like. 
     The additive material can be a transition metal, a rare-earth element, or the like. Note that specific examples of the additive material are as follows: cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), terbium (Tb), thulium (Tm), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), gold (Au), platinum (Pt), manganese (Mn), and the like. 
     Note that specific examples of a combination of the base material and the additive material (base material:additive material) which is used for the light emitting layer  924  are as follows: zinc sulfide (ZnS) and manganese (Mn) (ZnS:Mn), strontium sulfide (SrS) and cerium (Ce) (SrS:Ce), zinc sulfide (ZnS) and terbium (Tb) (ZnS:Tb), and the like. 
     The light emitting layer  924  can be formed by a film formation method such as a CVD method or a sputtering method. Note that the thickness of the light emitting layer  924  is 50 nm to 300 nm, preferably 100 nm to 200 nm. 
     Next, a fifth insulating film  925  which functions as the other insulating film of the light emitting element is formed over the light emitting layer  924 . Note that the fifth insulating film  925  is formed by a film formation method such as a plasma CVD method or a sputtering method to have a single-layer or stacked structure using an insulating film containing silicon such as a silicon oxide (for example, SiO 2 ) film, a silicon nitride (for example, Si 3 N 4 ) film, a silicon nitride oxide film, or a silicon oxynitride film, or an insulating film of metal oxide (for example, Al 2 O 3  or BaTiO 3 ) or the like. Note that the thickness of the fifth insulating film  925  is 50 nm to 250 nm, preferably 100 nm to 200 nm. 
     Next, a fourth conductive film  926  is formed over the fifth insulating film  925  ( FIG. 10C ). The fourth conductive film  926  can be formed using a film formation method such as a sputtering method, a PVD method, a CVD method, a droplet discharge method, an ink-jet method, or a printing method. Note that the thickness of the fourth conductive film  926  is preferably 50 nm to 400 nm, more preferably 100 nm to 250 nm. 
     The fourth conductive film  926  can be formed using a conductive film including a semiconductor such as Si or Ge; a single-layer conductive film of a metal element such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, or Nd; a stacked conductive film of a combination of a plurality of the above metal elements; a conductive film made of an alloy which includes the metal element as its main component (such as an aluminum-titanium alloy film); a conductive film made of metal nitride using the metal element; or the like. Alternatively, it may be formed using a conductive film of indium tin oxide (ITO), indium zinc oxide (IZO) formed using a target in which indium oxide containing silicon oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, indium tin oxide containing silicon oxide as a component (ITSO), or the like. Note that the above metal element in paste form may be used when using an ink-jet method. 
     The above-described third conductive film  919  serves as one electrode of the light emitting element. On the other hand, the fourth conductive film  926  serves also as the other electrode of the light emitting element. Therefore, when the fourth conductive film  926  is required to have a function as an electrode through which light obtained in the light emitting layer of the light emitting element is extracted, a material with high transmittance (for example, 40% or higher) with respect to visible light is preferably selected from the above materials to form the fourth conductive film  926 . When the fourth conductive film  926  is formed as an electrode through which light does not need to be extracted, a material with low transmittance (for example, lower than 10%) with respect to visible light or a material with high reflectance (for example, 40% or higher) is preferably selected from the above materials to form the fourth conductive film  926 . 
     In the present invention, unlike in the case described above with reference to  FIG. 10B , it is possible as shown in  FIG. 11A  that a second semiconductor film  928  is formed in advance using a material for forming a light emitting layer; seventh masks  929   a ,  929   b , and  929   c  are formed over the second semiconductor film  928 ; and second semiconductor films  931   a ,  931   b , and  931   c  which function as carrier supply layers can be formed by adding an n-type or p-type impurity element to parts of the second semiconductor film  928  with the seventh masks  929   a ,  929   b , and  929   c  present. Therefore, regions to which the n-type or p-type impurity element is not added function as light emitting layers  930   a ,  930   b , and  930   c.    
     Note that in the case of employing the manufacturing method shown in  FIGS. 11A and 11B , the second semiconductor film  928  needs to be formed using the same material as that of the light emitting layer  924  described with reference to  FIG. 10C  (the material including the base material that is a semiconductor and the additive material that is a light emitting center). Note that since specific examples of the material used to form the light emitting layer  924  are given above in this embodiment mode, the explanation is omitted here. 
     The specific material mentioned above as the impurity element which imparts n-type or p-type conductivity to the second semiconductor film  921  with reference to  FIG. 10B  can be used as the n-type or p-type impurity element added to the parts of the second semiconductor film  928  in  FIG. 11A . Note that specific examples of these impurity elements are also given above in this embodiment mode; therefore, the explanation is omitted here. 
     A fifth insulating film  932  and a fourth conductive film  933  are sequentially stacked over the second semiconductor films  930   a ,  930   b , and  930   c  functioning as the light emitting layers and the second semiconductor films  931   a ,  931   b , and  931   c  functioning as the carrier supply layers. Note that the fifth insulating film  932  formed here can be formed by a similar method and using a similar material to those of the fifth insulating film  925  described with reference to  FIG. 10C . The fourth conductive film  933  can be formed by a similar method and using a similar material to those of the fourth conductive film  926  described with reference to  FIG. 10C . Therefore, refer to the above description, and the explanation is omitted here. 
     As described above, the light emitting device described in this embodiment mode includes the light emitting element of the present invention, and in the light emitting element of the present invention, the efficiency of carrier supply to the light emitting layer can be increased. Therefore, the light emitting device has features of not only low drive voltage but also high resistance to deterioration. Accordingly, a light emitting device which consumes less power and has higher reliability than a conventional one can be obtained. 
     Embodiment Mode 5 
     This embodiment mode describes an active-matrix light emitting device which includes the light emitting element formed according to the present invention in a pixel portion, with reference to  FIGS. 12A and 12B . Note that the light emitting device of the present invention includes, as a component, the light emitting element of the present invention and a controller of a driver circuit which drives the light emitting element, or the like. 
     Note that  FIG. 12A  is a top view showing the light emitting device and  FIG. 12B  is a cross-sectional view of  FIG. 12A  taken along a line A-A′. 
     As shown in  FIG. 12A , there are a driver circuit portion (source side driver circuit)  1202 , a driver circuit portion (gate side driver circuit)  1203 , and a pixel portion  1204  over an element substrate  1201 . A reference numeral  1205  denotes a sealing substrate;  1206 , a sealant; and  1207 , a space surrounded by the sealant  1206 . 
     Note that a lead wiring  1218  ( FIG. 12B ) is a wiring for transmitting signals to be inputted to the source side driver circuit  1202  and the gate side driver circuit  1203  and receives a video signal, a clock signal, a start signal, a reset signal, and the like from an FPC (Flexible Printed Circuit)  1208  that serves as an external input terminal. Note that only the FPC is shown here; however, the FPC may be provided with a printed wiring board (PWB). The light emitting device in this specification includes not only a main body of the light emitting device but also the light emitting device with an FPC or a PWB attached. 
     Next, a cross-sectional structure is described with reference to  FIG. 12B . The driver circuit portions and the pixel portion are formed over the element substrate  1201 . Here, the source side driver circuit  1202  that is the driver circuit portion and the pixel portion  1204  are shown. 
     Note that a CMOS circuit that is a combination of an n-channel TFT  1209  and a p-channel TFT  1210  is formed as the source side driver circuit  1202 . The driver circuit may be a CMOS circuit, a PMOS circuit, or an NMOS circuit. A driver integration type in which a driver circuit is formed over a substrate is described in this embodiment mode, but it is not necessarily required and a driver circuit can also be formed not over a substrate but outside a substrate. 
     The pixel portion  1204  includes a plurality of pixels, each of which includes a switching TFT  1211 , a driving TFT  1212 , and a first electrode  1213  which is electrically connected to a drain of the driving TFT  1212 . Note that an insulator  1214  is formed to cover an end portion of the first electrode  1213 . 
     A layer  1215  in which a light emitting layer and a carrier supply layer are interposed between two insulating films, and a second electrode  1216  are formed over the first electrode  1213 . 
     The light emitting layer included in the layer  1215  can be formed by a CVD method, a PVD method, a sputtering method, an evaporation method, an ink-jet method, or the like. The light emitting layer and the carrier supply layer can be formed using the materials which are described in Embodiment Mode 1. 
     In other words, the active-matrix light emitting device in this embodiment mode has a structure as described in Embodiment Mode 1, that is, a structure having a light emitting element  1217  including the layer  1215  in which the light emitting layer and the carrier supply layer are interposed between insulating films, between the first electrode  1213  and the second electrode  1216 . 
     Although  FIG. 12B  shows only one pixel, a plurality of pixels is formed in matrix in the pixel portion  1204 . Note that the active-matrix light emitting device may have a structure in which different materials are appropriately used for light emitting layers so that pixels show light emission of different colors (for example, red (R), green (G), and blue (B)), or a structure combined with a color conversion layer or a color filter. 
     By attachment of the sealing substrate  1205  to the element substrate  1201  with the sealant  1206 , the light emitting element  1217  is provided in the space  1207  surrounded by the element substrate  1201 , the sealing substrate  1205 , and the sealant  1206 . Note that the space  1207  may be filled with an inert gas (such as nitrogen or argon) or the sealant  1206 . 
     As the sealing substrate  1205 , a plastic substrate formed of FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar, polyester, acrylic, or the like can be used besides a glass substrate or a quartz substrate. 
     As described above, the light emitting device includes the light emitting element of the present invention, and in the light emitting element of the present invention, the efficiency of carrier supply to the light emitting layer can be increased. Therefore, the light emitting device has features of not only low drive voltage but also high resistance to deterioration. Accordingly, a light emitting device which consumes less power and has higher reliability than a conventional one can be obtained. 
     Note that the light emitting device described in this embodiment mode can be freely combined with any of the structures described in Embodiment Modes 1 to 4. 
     Embodiment Mode 6 
     This embodiment mode describes a passive-matrix (simple-matrix) light emitting device which is formed according to the present invention, with reference to  FIGS. 13A to 13D . 
     The passive-matrix light emitting device of the present invention has a structure, as shown in a perspective view of  FIG. 13A , in which a plurality of first electrodes  1302  each serving as one electrode of a light emitting element is separately formed in stripes over a first substrate  1301 , a layer  1303  in which a light emitting layer and a carrier supply layer are interposed between insulating films is formed over the first electrodes  1302 , and a plurality of second electrodes  1304  is separately formed in stripes over the layer  1303  so as to intersect with the first electrodes  1302 . 
     Note that the first electrodes  1302  and the second electrodes  1304  can be formed using a film formation method such as a sputtering method, a PVD method, a CVD method, a droplet discharge method, an ink-jet method, or a printing method. Note that the thickness of each of the first electrodes  1302  and the second electrodes  1304  is preferably 100 nm to 400 nm, more preferably 150 nm to 250 nm. 
     The first electrodes  1302  and the second electrodes  1304  can be formed using a conductive film including a semiconductor such as Si or Ge; a single-layer conductive film of a metal element such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Zr, Ba, or Nd; a stacked conductive film of a combination of a plurality of the above metal elements; a conductive film made of an alloy which includes the metal element as its main component (such as an aluminum-titanium alloy film); a conductive film made of metal nitride using the metal element; or the like. Alternatively, they may be formed using a conductive film of indium tin oxide (ITO), indium zinc oxide (IZO) formed using a target in which indium oxide containing silicon oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, indium tin oxide containing silicon oxide as a component (ITSO), or the like. 
     For either of the first electrodes  1302  or the second electrodes  1304  which are required to have a function as electrodes through which light obtained in the light emitting layer of the light emitting element is extracted, a material with high transmittance (for example, 40% or higher) with respect to visible light is preferably selected from the above materials to form either of the first electrodes  1302  or the second electrodes  1304 . For electrodes through which light does not need to be extracted, a material with low transmittance (for example, lower than 10%) with respect to visible light or a material with high reflectance (for example, 40% or higher) is preferably selected from the above materials to form the electrodes. 
     Note that a light emitting element is formed in each position where the first electrode  1302  overlaps with the second electrode  1304  with the layer  1303  interposed therebetween (for example, a region a ( 1305 ) shown in  FIG. 13A ). 
     A structure of the light emitting element in the region a ( 1305 ) is shown in  FIG. 13B . In other words, the layer  1303  interposed between the first electrodes  1302  and the second electrodes  1304  includes a first insulating film  1306 , a layer  1307  including a light emitting layer and a carrier supply layer, and a second insulating film  1308 . 
     Note that the first insulating film  1306  and the second insulating film  1308  are formed by a film formation method such as a CVD method or a sputtering method to have a single-layer or stacked structure using an insulating film containing silicon such as a silicon oxide (for example, SiO 2 ) film, a silicon nitride (for example, Si 3 N 4 ) film, a silicon nitride oxide film, or a silicon oxynitride film, or an insulating film of metal oxide (for example, Al 2 O 3  or BaTiO 3 ) or the like. Note that the thickness of each of the first insulating film  1306  and the second insulating film  1308  is 10 nm to 250 nm, preferably 100 nm to 200 nm. 
     The layer  1307  including a light emitting layer and a carrier supply layer preferably has a structure as shown in  FIG. 13C . In other words, the layer  1307  including a light emitting layer and a carrier supply layer preferably has a structure in which a plurality of carrier supply layers  1310  is separately formed in a light emitting layer  1309  and each distance between the adjacent carrier supply layers  1310  is short. For example, the layer  1307  preferably has a structure in which the carrier supply layers  1310  are formed in stripes as shown in  FIG. 13C , or a structure in which the carrier supply layers  1310  are formed in matrix as shown in  FIG. 13D . 
     Note that the light emitting layer  1309  and the carrier supply layers  1310  can be formed by a film formation method such as a CVD method or a sputtering method, and the thickness of each of them is preferably 50 nm to 300 nm, more preferably 100 nm to 200 nm. 
     The light emitting layer  1309  can be formed to include a base material that is a semiconductor and an additive material that is a light emitting center. Specific examples of the base material and the additive material can be the materials described in Embodiment Mode 4. Therefore, refer to the above description, and the explanation is omitted here. 
     The carrier supply layers  1310  can be formed using a semiconductor material which includes indium (In), aluminum (Al), gallium (Ga), silicon (Si), or the like as an n-type impurity element or nitrogen (N), phosphorus (P), zinc (Zn), or the like as a p-type impurity element. 
     Note that the structures shown in  FIGS. 13C and 13D  facilitate induction of carriers supplied from the carrier supply layers  1310  to an interface between the light emitting layer  1309  and the insulating film (the first insulating film  1306  or the second insulating film  1308 ) and can improve luminous efficiency of the light emitting element. 
     Embodiment Mode 7 
     Examples of electronic devices each having the light emitting device of the present invention are as follows: a television device (also referred to as simply a television, or a television receiver), a camera such as a digital camera or a digital video camera, a telephone set (simply also referred to as a telephone or a phone), an information terminal such as PDA, a game machine, a computer monitor, a computer, a sound reproducing device such as a car audio system or an MP3 player, an image reproducing device including a recording medium, such as a home-use game machine, and the like. Preferred modes of them are described with reference to  FIGS. 14A to 14E . 
       FIG. 14A  shows a television device according to the present invention, which includes a main body  8001 , a display portion  8002 , and the like. In this television device, the light emitting device of the present invention including the light emitting element having features of not only high luminous efficiency and low drive voltage but also high resistance to deterioration is applied to the display portion  8002 . Therefore, a television device which consumes less power and has higher reliability than a conventional one can be provided. 
       FIG. 14B  shows an information terminal device according to the present invention, which includes a main body  8101 , a display portion  8102 , and the like. In this information terminal device, the light emitting device of the present invention including the light emitting element having features of not only high luminous efficiency and low drive voltage but also high resistance to deterioration is applied to the display portion  8102 . Therefore, an information terminal device which consumes less power and has higher reliability than a conventional one can be provided. 
       FIG. 14C  shows a digital video camera according to the present invention, which includes a main body  8201 , a display portion  8202 , and the like. In this digital video camera, the light emitting device of the present invention including the light emitting element having features of not only high luminous efficiency and low drive voltage but also high resistance to deterioration is applied to the display portion  8202 . Therefore, a digital video camera which consumes less power and has higher reliability than a conventional one can be provided. 
       FIG. 14D  shows a telephone according to the present invention, which includes a main body  8301 , a display portion  8302 , and the like. In this telephone, the light emitting device of the present invention including the light emitting element having features of not only high luminous efficiency and low drive voltage but also high resistance to deterioration is applied to the display portion  8302 . Therefore, a telephone which consumes less power and has higher reliability than a conventional one can be provided. 
       FIG. 14E  shows a liquid crystal monitor according to the present invention, which includes a main body  8401 , a display portion  8402 , and the like. In this liquid crystal monitor, the light emitting device of the present invention including the light emitting element having features of not only high luminous efficiency and low drive voltage but also high resistance to deterioration is applied to the display portion  8402  as a backlight. Therefore, a liquid crystal monitor which consumes less power and has higher reliability than a conventional one can be provided. 
     As described above, the applicable range of the light emitting device of the present invention is so wide that the light emitting device can be applied to electronic devices of various fields. With the use of the light emitting device of the present invention, an electronic device having a display portion which consumes less power and has high reliability can be provided. 
     This application is based on Japanese Patent Application serial no. 2006-043624 filed in Japan Patent Office on Feb. 21, 2006, the entire contents of which are hereby incorporated by reference.