Semiconductor device and method for producing the semiconductor device

Abstract: While producing a III-V compound semiconductor layer, carbon is added to group III and V elements to control the p type conductivity of the semiconductor layer, forming a p type region. Then, a small amount of n type dopant is added to the group III and V elements together with the carbon to control the n type conductivity of the semiconductor layer, forming an n type region. Therefore, a sharp and precisely-controlled doping profile is obtained in the vicinity of the p-n junction, resulting in a semiconductor device having high initial-performance and high reliability.

Description: FIELD OF THE INVENTION The present invention relates to a III-V compound semiconductor device including a p-n junction and a method for producing the semiconductor device. BACKGROUND OF THE INVENTION Figure 5 is a perspective view showing a laser diode disclosed in Mitsubishi Denki Giho Vol. 62, No. 11 (1988), pp. 28-31 as an example of a prior art III-V compound semiconductor device having a p-n junction. In figure 5, reference numeral 1 designates an n type GaAs substrate. An n type AlGaAs first cladding layer 2 is disposed on the substrate 1. A p type AlGaAs active layer 3 is disposed between the n type AlGaAs first cladding layer 2 and a p type AlGaAs second cladding layer 4 which have lower refractive indices than that of the active layer. The p type AlGaAs second cladding layer 4 has a stripe-shaped ridge structure. A p type GaAs buffer layer 5 and an n type GaAs current blocking layer 6 are disposed on opposite sides of the ridge structure. A p type GaAs contact layer 7 is disposed on the ridge structure and the n type GaAs current blocking layer 6. A stripe-shaped positive electrode 8 is disposed on the p type GaAs contact layer. The conductivity type of the GaAs buffer layer 5 gradually changes from n to p upwardly so that the regrowth surface of the p type AlGaAs second cladding layer 4 may not contact with the n type GaAs current blocking layer, whereby the current blocking characteristic is improved. A negative electrode 9 is disposed on the rear surface of the n type GaAs substrate 1. Selenium (Se) and zinc (Zn) are used as n type and p type dopants, respectively. A description is given of the operation. When plus and minus voltages are applied to the positive and negative electrodes 8 and 9, respectively, to bias a p-n junction of the p type AlGaAs active layer 3 and the n type AlGaAs first cladding layer 2 in a forward direction, high-concentration electrons and holes are injected into the p type AlGaAs active layer 3 from the cladding layers 2 and 4. The injected carriers are confined by a barrier of a heterojunction between the n type AlGaAs first cladding layer 2 and the p type AlGaAs active layer 3 and recombined with a high efficiency in the active layer 3, generating laser light. A greater part of the laser light generated by the recombination of carriers is confined in the active layer 3 due to a difference in refractive indices between the active layer 3 and the cladding layers 2 and 4. At this time, a light emitting region is limited to the center of the active layer 3 due to the current concentrating effect of the current blocking layer 6. Figure 6 illustrates SIMS (Secondary Ion Mass Spectroscope) profiles of selenium (Se) and zinc (Zn) in the vicinity of the active layer 3. Figure 7 illustrates SIMS profiles of n type and p type carrier concentrations. The laser diode shown in figure 5 is fabricated using an epitaxial growth method and when the AlGaAs first cladding layer 2 is grown, Se is doped to a concentration of 10 17 cm -3 level or more as an n type dopant. During the epitaxial growth, if an attention is given to a crystal growth of As, Se atoms fill vacancies V As , which are originally to be filled with As atoms, and act as n type dopant as represented by the following reaction formula (1). On the other hand, when the n type AlGaAs first cladding layer 2 and the p type AlGaAs active layer 3 are grown, Zn is doped to a concentration of 10 17 cm -3 level or more as a p type dopant. At this time, if an attention is given to a crystal growth of Ga, Zn atoms fill vacancies V Ga , which are originally to be filled with Ga atoms, and act as a p type dopant as represented by the following reaction formula (2). As described above, each of Se and Zn is doped to a concentration as high as or higher than 10 17 cm -3 level to produce the p-n junction, so that a mutual diffusion occurs at the p-n interface and the profile of the carrier concentration at the p-n interface is not sharp as shown in figure 7. In figures 6 and 7, a.u. means an arbitrary unit. In the above-described laser diode, sharpness and controllability of the doping profile are poor, which deteriorates initial performance and reliability of a completed device. In order to realize a sharp profile of the carrier concentration at the p-n interface, following methods have been proposed. In Japanese Published Patent Application No. 60-167417, a conductivity type of a semiconductor layer is controlled not by doping impurities but by changing composition ratio of group III compound semiconductor and group V compound semiconductor. In Japanese Published Patent Applications Nos. 2-203520 and 3-4517, a vapor phase growth is carried out using trimethylgallium as a dopant gas including group III element and arsine as a dopant gas including group V element. During the growth, ratio of concentrations of these gases is controlled to incorporate carbon atoms with Ga atoms, whereby the carbon atoms function as a p type dopant. In Japanese Published Patent Application No. 63-143810, a vapor phase growth is carried out using trimethylgallium as a dopant gas including group III element and arsine as a dopant gas including group V element. During the growth, a p type region is formed by incorporating carbon atoms with Ga atoms and an n type region having a desired carrier concentration is formed by As and Se, resulting in a p-n junction. In the above-described conventional methods, however, it is necessary to largely change the growth condition to control the conductivity type of the semiconductor layer, such as a change of ratio of concentrations of the dopant gases, so that the crystal growth is not favorably carried out at the p-n interface. In addition, when the growth condition changes, the vacancies may remain on the growth surface of the substrate without being filled with the carbon atoms. Such imperfect crystal growth and vacancies deteriorate characteristics of the device, resulting in a poor initial-performance and a poor reliability. SUMMARY OF THE INVENTION It is an object of the present invention to provide a III-V compound semiconductor device that ensures a sharp and precisely-controlled doping profile, favorably grown crystal at the p-n interface, good initial-performance, and high reliability. It is another object of the present invention to provide a production method for such a semiconductor device. Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter. The above objects are achieved by a device according to Claim 1, and by a method of producing such a device according to Claim 2. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1(a)-1(c) are diagrams for explaining a crystal growth in the vicinity of an active layer of a laser diode in accordance with a first embodiment of the present invention, in which figure 1(a) is a sectional view and figures 1(b) and 1(c) are schematic diagrams showing atomic arrangements; Figure 2 is a diagram showing SIMS profiles of carbon and selenium in the structure shown in figure 1(a); Figure 3 is a diagram showing SIMS profiles of n type and p type carrier concentrations in the structure shown in figure 1(a); Figure 4 is a diagram showing a relation between a quantity of carbon doped into AlGaAs and a carrier concentration in accordance with the first embodiment of the present invention; Figure 5 is a perspective view of a laser diode in accordance with the prior art; Figure 6 is a diagram showing SIMS profiles of selenium and zinc in the vicinity of the active layer of the laser diode shown in figure 5; and Figure 7 is a diagram showing SIMS profiles of n type and p type carrier concentrations in the vicinity of the active layer of the laser diode shown in figure 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1(a)-1(c) are diagrams for explaining a crystal growth in the vicinity of an active layer of a laser diode in accordance with a first embodiment of the present invention. More specifically, figure 1(a) is a sectional view showing the active layer and its vicinity and figures 1(b) and 1(c) are schematic diagram showing atomic arrangements in production process. In figure 1(a), a p type AlGaAs active layer 30 is disposed between an n type AlGaAs first cladding layer 20 and a p type AlGaAs second cladding layer 40. In figures 1(b) and 1(c), Ga is used as group III atoms and As is used as group V atoms, and Al is omitted for simplification. Figure 2 illustrates SIMS profiles of carbon and selenium in the structure of figure 1(a) and figure 3 shows SIMS profiles of n type and p type carrier concentrations in the structure of figure 1(a). A description is given of the production method. First, the n type AlGaAs first cladding layer 20 is grown by vapor deposition. Trimethylgallium and trimethylaluminum are employed as group III materials and arsine is employed as a group V material. Hydrogen-diluted selenium (H 2 Se) gas or the like is used as a source of selenium and selenium is doped to a concentration of 1 X 10 16 cm -3 . Trimethylarsenic (TMAs) gas, carbon tetrachloride (CCl 4 ) gas, or the like is employed as a source of carbon and carbon is doped to a concentration of 2 X 10 17 cm -3 . A growth temperature is about 800°C and a pressure in a reaction tube is about 133 hPa (100 Torr). During the growth, carbon atoms, which should originally fill group V lattice sites and function as a p type dopant, fill group III lattice sites and function as n type dopant because the V lattice sites are filled with selenium atoms as shown in figure 1(b). This reaction is represented by the following formula (3). At this time, 10 17 to 10 18 selenium atoms per 1 mol fill group V lattice sites and approximately the same number of carbon atoms fill group III lattice sites. In this way, the n-type Al 0.48 Ga 0.52 As first cladding layer 20 about 1.5 micrometers thick is formed. Although the carbon atoms are not likely to fill the III lattice sites usually, the presence of the selenium atoms in the V lattice sites causes the carbon atoms to fill the III lattice sites. When the p type AlGaAs active layer 30 is grown, the supply of H 2 Se is stopped and the supply of trimethylaluminum gas is decreased. Then, the selenium atoms are gone in the reaction gas, so that the carbon atoms begin to fill V lattice sites as shown in figure 1(c) and function as a p-type dopant. This reaction is represented by the following formula (4). At this time, 10 17 to 10 18 carbon atoms per 1 mol fill group V lattice sites. In this way, the p type Al 0.1 Ga 0.9 As active layer 30 approximately 30 nanometers thick is formed. Thereafter, the supply of trimethylaluminum gas is again increased to grow the p-type Al 0.48 Ga 0.52 As second cladding layer 40 approximately 1.5 micrometers thick. As shown in figure 3, the SIMS profile of the carrier concentration in the vicinity of the active layer 30 has a sharp change at the boundary between the active layer 30 and the first cladding layer 20. That is, the carbon atoms, continuously supplied during the growth process, function as a p-type dopant in the first cladding layer 20 while function as an n-type dopant in the active layer 30 and the second cladding layer 40. As shown in figure 4, the carrier concentration is arbitrarily changed by increasing the amount of selenium or carbon doped into AlGaAs. In addition, when the amount of carbon is increased to a certain degree, the n-type carrier concentration decreases and a nature of carbon as a p-type dopant appears, whereby a maximum amount of carbon to serve as an n-type dopant is found. According to the present invention, when carbon and a small amount of selenium which fills group V lattice sites and functions as an n-type dopant are introduced into a reaction tube together with the source gases including group III and V atoms, the carbon, which functions as a p-type dopant when selenium is not applied, functions as an n-type dopant. Therefore, the growth condition is not changed so much as compared with the conventional method of changing the supply ratio of the group III and V gases to obtain a p-type doping profile, so that an improved crystal growth is carried out. In addition, the control of both p-type and n-type conductivities is carried out by applying carbon having a small diffusion coefficient, so that a mutual diffusion at the p-n interface is reduced and a very sharp and precise carrier profile is achieved as designed. In case of laser diode, initial performance and reliability are significantly improved. While in the above-illustrated embodiment the AlGaAs laser diode is employed as an example of a semiconductor device, the present invention may be applied to other III-V compound semiconductor devices having p-n junctions, such as a HEMT, a heterojunction bipolar transistor, or the like. While in the above-illustrated embodiment Ga and As are employed as the group III element and the group V element, respectively, other III and V elements may be employed. In addition, although selenium is used as an element added to the source gases together with carbon, tellurium (Te) or sulfur (S) may be employed. As is evident from the foregoing description, according to the III-V compound semiconductor device of the present invention, carbon is added to the source gases for producing the III-V compound semiconductor layer, so that carbon atoms fill group V lattice sites, thereby controlling the p-type conductivity. A small amount of n-type dopant is added together with the carbon, so that the carbon atoms fill group III lattice sites, thereby controlling the n-type conductivity. Therefore, a steep doping profile is obtained in the vicinity of a p-n interface, so that a precisely-controlled heterojunction is achieved as designed, resulting in a compound semiconductor device having high initial-performance and high reliability.

Claims: A III-V compound semiconductor device including a p-n junction comprising a p-type region in which the group III/V host lattice is doped with carbon atoms, and an n-type region in which the group III/V host lattice is doped with selenium(Se) atoms, tellurium(Te) atoms and/or sulfur(S) atoms and with carbon(C) atoms wherein the Se, Te and/or S dopant atoms push the C dopant atoms from the group V lattice sites to group III lattice sites, thereby both the Se, Te and/or S atoms serving as n-type dopants. A method of producing a III-V compound semiconductor device having a p-n junction by vapor deposition using a first gas including group III atoms and a second gas including group V atoms, comprising: adding a carbon-containing gas to said first and second gases in a sufficient amount that the semiconductor comprises 10 17 - 10 18 carbon atoms per mol to form a p-type region; and adding selenium, tellurium and/or sulfur as n-type dopant to said first and second gases in a sufficient amount that the semiconductor comprises 10 17 to 10 18 atoms of selenium, tellurium and/or sulfur per mol of the group III/V host lattice and to said carbon-containing gas which latter is comprised in a sufficient amount that the semiconductor comprises 10 17 to 10 18 carbon atoms per mol of the group III/V host lattice to form an n-type region whereby the Se, Te and/or S dopant atoms push the C dopant atoms from the group V lattice sites to group III lattice sites, thereby both the Se, Te and/or S atoms serving as n-type dopants. The method of claim 2 wherein said p-type region is formed by depositing the group III atoms included in said first gas with the group V atoms included in said second gas and doping the compound semiconductor crystal lattice with the carbon atoms which occupy group V lattice sites, and said n-type region is formed by depositing the group III atoms with the group V atoms and doping the semiconductor crystal lattice with the carbon atoms which occupy group III lattice sites and with the Se, Te and/or S atoms which occupy group V lattice sites.

Inventors: HAYAFUJI NORIO, HAYAFUJI, NORIO, HAYAFUJI, NORIO, MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: H01L21
IPC codes: H01L29, H01L21, H01S5