HIGH POWER LASER DIODE

Abstract: High power laser diode consisting of a limiting, a main, an intermediate, an active, and an excitation region, which has a confining factor comprised between 1.5*10<-4> and 1.5*10<-3> and a resonator length comprised between 1.5 and 3 cm, wherein, due to a small refractive index difference between the main and limitation regions, only the fundamental transverse mode, which has the maximum of the flux density situated in the main region, can propagate.

Description: HIGH POWER LASER DIODE FIELD OF THE INVENTION This invention relates to high power laser diodes which can be Ltsed for laser emission at increased densities of the radia¬ tion -flu * : and in the fundamental transverse mode. BACKGROUND OF THE INVENTION There us known that the increased radiation flu:: density o— peration of laser diodes is limited by the catastrophic degrada¬ tion, phenomenon wherein the semiconductor material ot the active region, situiated at the semiconductor material-external medium interface, this interface being also the mirror of the Fabry- Perot resonator, is subjected to an excessive heating produced by laser radiation abεorbtion near the interface. Due to this exces¬ sive heating, the resonator mirror can be destroied by local melting. The destruction starts with the band to band absorbtion of the laser radiation flux near the surface, this absorbtion prevailing over the gain due to the decrease of the free carrier concentration toward the surface as t e result of the fast surface nonradiative recombination phenomena. The absorbtion of the laser radiation flux, followed by the dissipation of the absorbed energy in nonradiative processes, produces an initial local heating which in its turn induces the decrease of the band gap and, -further on, the increase of absorbtion and heating phenomena rates etc. When a critical value of this local heating is exceeded, the absorbtion and heating processes succeed each other so fast that they lead to the catastrophic degradation phenomenon, the intensity of which depends on the magnitude of the surface recombination rates and on the magnitude of tne laser radiation flux density reaching the surface and being absorbed. The majority of laser diodes are fabricated from a succes sion of epitaxial, parallel layers, including the active layer, and the Fabry—Perot resonator mirrors are obtained by cleavin the semiconductor crystal perpendicular to the plane of the epi taxial layers, so that they inherently conserve the disadvantag of the catastrophic degradation at relatively small radiatio flux densities, due to high value of the surface recombination at the active region—external medium interface. There are also known laser diodes with transparent mirror whereat the radiation flu:: density can be increased by dimini shing the surface recombination rate and the influence of mirror absorbtion mechanisms. Such a type of laser diodes presents an active region terminated in the mirror vecinity with a transpa rent semiconductor material , with a larger than that of the acti ve region band gap, so that the absorbtion mechanisms at th semiconductor material-external medium interface are completel eliminated and, at the active region-transparent mediu interface, the interface recombination rate is reduced, th decrease of the carri er concentration i _ also reduced, so tha the interface absorbtion of the incident flu:; on the interface i also reduced. Transparent mirror laser diodes have the disadvantage tha for fabricating the transparent region microlithographic, etchin and epitaxial growth processe are needed and the mirrors need t be produced by cleaving in a relativelv narrow, 20 - 50 y wid region. Laser diodes .Sreat Britain Patent BB 2031644 A) formed fro structures with 4 or 5 layers wherein one of the layers is use mainly as a waveguide and I≡ adjoined to the active layer or I separated -rrom this one b-- £? carrier confinement iaver sc tha the radiation flux i. distributed both in the active layer and i the waveguide are also I πown. These diodes present th disadvantage that the thic. ness of the waveguide is not greate than 2 urn and that the operation in higher order transverse mod in the widest proposed waveguides is possible. SUMMARY OF THE INVENTION The aim of this invention is to fabricate laser diodes wit as high as possible values for the flux density and for the tota em. tted f] ux. The problem which is solved by this invent] on is to fabrica te laser diodes formed bv epitaxial, parallel between the tw mirrors, layers, with the waveqmde main region separated fro the active one, diodes hav * ng a very small magnitude of th radiation flux in the active region. The high power laser diode according to the inventio resolves this problem using a structure consisting of substrate, a limitation region, <* main region, an intermediat re-ςuon, an active region, on excitati n region and a contac region, wherein the refractive index QT the active region is th hiqhest in the structure, wherein the refractive index of th main region is the next lπ.eπor one, wherein the product ot th active region thickness by the square root of the difference of the squares of the refractive indexes o+ active, respectivel main regions is smaller than _.> quarter of the vacuum wavelengt of the laser radiation, wherein excitation and intermediat regions have conductivity types: opposite to each other, in orαer to opperat at high radiation Mux densities and to allow on] ths propagation of the fundamental transversε mode the maximum radiation +lu; ot which τ z located in the ma n region and tne e-t+ecti v-e retractive inαε,, or which is comprised between the refractive index values of the limitation and of the main regions, the product of the main region thickness by the square root of the difference of the squares of retractive indexes of the main, respectively limitation regions s smaller than half the vacuum wavelength of laser raoiation, the difference between the refractive indexes of the main and limitation regions is obtained only by different dopping concentrations o+ these regions, the difference in carrier concentrations being comprised between 7 " _-10 and .9*10 cm " ' , correlated to the values for the main region thickness between 2 and 5 , r μm, the -4 -3 confinement factor is comprised between 1-5*10 and 1.5*l0 and the resonator leπth is comprised between 1.5 and 3 cm. BRIEF DESCRIPTION OF THE DRAWINGS Other features of the diode according to the invention will become apparent from the detailed description which follows, reference being made to FIG. 1...3 in which: FIG. 1 is a perspective view of the laser diode; FIG. 2 is a graph of the radiation flux density as a func¬ tion of the coordinate perpendicular to tne waveguide structure; FIG. is a graph of the refractive index of the semiconduc¬ tor materials as a function of the coordinate perpendicular to the waveguide structure. SPECIFIC DESCRIPTION The laser diode according to the invention, reference being made to FIG. 1, consists of the following layers; a substrate 1, a limitation region 2, a main region 3, an intermediate region 4, ar active region 5, an excitation region 6 and a contact region 7. The regions i...? consists of semiconductor materials. The external region 1 is covereα with a metallic contact S and the external region 7 with a metallic contac- 9. The metallic contacts 8 and 9 allow the flow of an electrical exciting curren through the laser diode when an external voltage eκt , with th proper polarity, is applied. The waveguide, consisting of region 2... , terminates at one side with a semiconductor material external medium interface .10 and at the other side with semiconductor material-external medium interface 11. These tw interfaces are plan parallel to each other and perpendicular t the waveguide structure and represent the Fabry-Perot resonato mirrors. The spatial disposal of the laser diode presented in FIG. is refered to an orthogonε.1 coordination system Oxys. For simpli city a laser diode with a very large width w in the y directio is considered and the laser radiation along the y direction i supposed uniform. The radiation propagates along the waveguide i z direction. The mirrors 10 and 11 are parallel to the xy plane. A cross-section parallel to the xy plane is considered. I this cross section, the radiation flux density has a dependenc determined by a 1=1 (x) function on the x coordinate perpendicula to the waveguide structure. In FIG. 2 a graph 12 which represent the I («) function in a (I,x) coordinate system is shown. Th shape of the graph is the same in every transverse cross-sectio parallel to the xy plane. A flux df is passing through the w*d area of the transverse cross-section: df=I(x)*w*dx (1) The limitation region 2 extends from a coordinate x _ to coordinate 2* the main region 3 from __ e coordinate 2 to coordinate T;, the intermediate region 4 from the coordinate 3 to a coordinate X4, the active region 5 from the coordinate to a coordinate 5, the excitation region from the coordinate X5 to a coordinate ^ and the contact region from the coordinate x^ to a coordinate x-γ. The active region thickness is d a _=X5~X and the main region thickness is cl r - 1 = 3~ 2_ The function I(x> has a maximum value of the radiation flux in the active region, I max , and a maximum value of the radiation flux density in the active region I m . a _. The sum of the flux density in the whole (x £ ,.' . interval of the laser diode structure determines a value of the total flux, F, and the sum of the flux density in the .X4,xg) interval deter¬ mines a value f a of the flux passing through the active region cross-section. The emitted flux passing through the active region, f a , is proportional to the double hatched area in FIG. 2 and the total radiation flux F passing through the whole cross- section is proportional to the hatched area, including the double hatched one. The confinement factor T is the subunitar ratio: f = f a /F (2) The 1=1 <x> function represented by the graph 12 is charac¬ teristic for the fundamental transverse mode propagation in the guide. For this mode the function has the main maximum value inside the main region and asymtoticaly decreases to zero in the excitation 6 and limitation 2 regions. The operation in the fun¬ damental transverse mode is important both for applications wherein laser diode radiation is transmited through optical fibers and for those wherein it is transmited into atmosphere through collimating systems. FIG. 3 presents a graph 13 of the dependence on the coordinate κ of the refractive index n of the semiconductor materials constituting the epitaxial structure in a coordinate system (n,x.. For simplicity, the refractive indexes are supposed constant in every region. In the following an algorithm for choosing the n j ...rι to is presented. The act ve region 5 has a value ng of the refractive ind which is the maximum value. The main region 3 has a value which is next inferior to the n_, value. The wave propagati speed, v, along the z direction in the waveguide is determined an effective index n e f+ such that v=c n e ^^, where c s t light propagation speed in vacuum. A relation between the acti region 5 thickness, d a , and the refractive index difference (n n > is imposed so that the propagation of any mode with effective refractive index value n e between n and ng values not possible. In connection with the vacuum l ser radiati wavelength Λ D , the conditioning relation for the cut off of t or, approximately: The intermediate reg on 4 has a refractive index value and the excitation region έ> a refractive index value n^,, valu firstly determined by the energy band gaps of the semiconduct mε-steπal- * consti uting the respective regions, energy band ga which should be high enough compared to the energy band gap the active region 5, to build effective potential barriers f the nonequi1lbπum carriers, electrons and holes, in their pat from the act ve region 5 toward the adjoining regions and t provide the carrier confinement effect. The regions adjoined to the active region 5, namely th intermediate region 4 ana the excitation region 6 hav conductvιt types, n or p, opposite- to each other, so tha between them there is a p-n junction for the active region excitation. The active region 5 has the conductivity type eithe n or p, or can consist of undoped semiconductor material, o l_ ca include the p-n junction. If the semiconductor material of the main region 3 has th band gap close to the band gap of the active region 5, then th intermediate region 4 should be thick enough in order to avoi the nonequi libri m carrier tunneling. The thickness of an effective potential barrier dependes on the carrier effectiv mass and on the barrier height which in its turn depends on th difference between the intermediate region 4 and the activ region 5 energy band gaps. For example, in order to have a tunneling transmissio coefficient through the intermediate region 4 barrier smalle than 10 ' , in the case of the carriers with the effective mas equal to 0,07 m e and of a barrier height equal to 140 meV, th intermediate region thickness should be larger than 0,03 m. Greater the intermediate region 4 thickness, (X4-X3) , greater is the radiation attenuation from the main maximum, situated in the main region, toward the active region and greate is the ratio r of the absolute maximum radiation flux densit •'■max * ' ° ^he maximum radiation flux density in the active regio ■l-m.a. ' r= "-'-max'-'-m. a. • ^- n " t e mean time, toghether with a high value, a high over unity ratio of the total radiation flux F t the active region flux f a , can be obtained. In thi way, toghether with a great ratio between the main and activ regions thicknesses, the intermediate region plays an essentia role in obtaining small values for F . The approximate relation between the total flux F and th maximum density of the radiation flux in the active region is: where K is a numerical coefficient between 0.5 and 1. The valu κ=0.5 can be used when the double natched area on FIG. 2 approximated by a triangle area, if the radiation does no penetrate in the excitation region, and the value . =1 can be use if the radiation is extending in the excitation region, due to relatively small difference between the ng and n^ values. The l m .a. value is limited by catastrophic degradatio phenomena. Informations about the maximum admissible value o ■_m.a. can be obtained from laser diode wherein the radiation flu is almost completely confineα in the active region .T =1). Fo the AlGaAs materials system and for continuous wave operation, *m.a. values of the order of 10 W/cm" are Inown. If I m . a . valu is limited, to obtain as high as possible values for F, as low a -4 possible values for Fare needed. Values for V from 1,5*10 to 1,5*10 " *' are proposed in this invention. The refractive index n2 of the limiting region 2 must be sufficiently close to the ri value in order to avoid the propagation of other than the fundamental transverse mode. The condition for higher order transverse mode cut off is expressed as a function of re-fraction indexes ri2-, r- , and ng and of the active region 5 and main region thicknesses, d s and d m , by the relation: Using the previous relation <3) , for the main region thickness d m a condition is imposed: m* VVπ * - 3 -n 2 < Λ 0 /2 (7) The main region 3 thickness, d m , is chooεe i from 2 to 5 urn, in relation to the desired width of the laser beam and to the desired total flux-. F-or these thicrneεses, 2 pm and 5 pm, the differences between the retractive indexes 3 and n should be —3 —3 ^ • MQ , respectively i.l*-10 " , tor a 0.9 , respective!/ O.'-fiO , tcr e O. rpm wavelength and -3 - 5.6-- O " pm wavelength. bo small differences between refractive indexes can be reproducibly produced by free carrier concentration variation rather than by composition variation. The concentration variation should be 7*10 cm ""' , respectively 1.1*10 ' cm '"' , for the 0.9 ιum 17 -3 17 -3 wavelength and 5.6*10 cm " , respectively 0.9*10 cm , for the .8 pm wavewlength. When the semiconductor material of the active region 5 is excited by the current flow through the p-n junction, in the active region 5 nonequi 1ibrium carriers, electron and holes, appear and they recombine by photon emission. The stimulated emission determines a gain coefficient of the active region, g a . The cut off condition for modes with n e f f between n3 and ng determines the spreading of the electromagnetic radiation outside the active region 5, mainly in the waveguide main region 3. Due to this spreading the wave in the guide has a modal gain coefficient 6 proportional to the intrinsec active region gain coefficient g a and to F : G=g a *P (8) Due to the low confinement factor rvalues, a very high excitation of the active region 5 is needed in order to obtain a modal gain coefficient to exceed the losses. Values in the order of magnitude of 1000 cm for the active region gain coefficient g a are proposed in this invention so that the active region 5 is highly excited by high concentrations of the nonequi 1 ibrium carriers, radiative recombination of which produces the stimulated emission. At the semiconductor material-external medium interfaces 10, respectively 11, nonradiative surface recombination processes ar produced, supplementary to the bul , radiative ones so that ther is a decrease toward the surface of the excitation level of th ,- ^ active region 5, expressed by the nonequi 1ibrium carri concentrations. This decrease determines the replacement of t wave amplification by its attenuation, due to absorbtion. T absorbtion generates nonequi1ibrium carriers in the vecinity the semiconductor material-external medium interfaces 10 and 11 carri ers, which nonradiatively reco bine on the surface an produce the initial local heating. The initial local heating i relatively small due to the separation, produced by th intermediate region 4, of the main region 3, wherein the almos entire laser radiation is nonabsorbely emitted at interfaces 1 and 11, from the active region 5, wherein, at interfaces 10 an 11, recombination and absorbtion processes occure. The loca heating of the active region 5 is proportional to the radiatio flux density in this region, which is small compared to th maximum radiation flux density. The local heating reaches th critical value for producing the catastrophic degradation at critical value I m , a , cr , of the maximum flux density in the activ region 5, critical value which is approximately equal to th radiation flux density which produces the catastrophi degradation for a diode wherein the maximum of the flux densit is in the active region. The maximum flux which can be obtained before the appearanc of catastrophic degradation can be derived from a formul analogous to (5): and smaller the F value greater the F cr value. The aim of the invention is to provide as great, as possibl laser radiation total flux using as small as possible F* values. Increasing in this way the limit for the catastrophic degradatio obviously appears another limitation, namely that due to activ region heating. The active region heating is produced by the dissipation of spontaneous recombination energy necessary to reach the threshold condition and by the Joule effect. The operation of the laser diode at relatively low current densities J s is needed in order to limit this heating. So, for a good electric to radiant energy conversion and for high radiation fluxes emission, low current density and high total current operation is needed, what implies the usage of a very long resonator length L. In this invention a resonator length between 1,5 and 3 cm is proposed, the length value being limited only by technological considerations. When the resonator length increases the transmission losses decrease. Resonators with the back mirror reflectivity Rj-=1, obtained by dielectric or dielectric-metals coatings, will be considered firstly. The other mirror reflectivity R2 can be the natural one or, by the mentioned coating methods, can be varied between large limits, for example between 0.01 and 0.62. Mirror losses can be expreεed by a loss coefficient B , given by the relation: 1 &=2_:*ι n .l/R • ιlR κ -2?> (10) For example, for L=2.3 cm, Ri=l and R2=0.01 P>-=1 c ■-m,„ ,, and for R =0.62 B=0.1 cm . There is known that greater than the wave attenuation coefficient * - * ^, in the cavitiy is the mirror loss coefficient B , greater is the efficiency for the extraction of the stimulated emission. good engineering value for their ratio is: Free carrier absorbtion lasses in the active region will be considered as the mai wave attenuation mechanism inside the waveguide. Other possible mechanisms are the attenuation due to free carrier absorbt on in the other waveguide regions and the attenuation due to the light scattering on inhomoqenitIes at. wavequide inter-faces or inside the wavequide. Free carrier absorbtion in the active region 5 determines an intrinsec absorbtion coefficient _ a . Due to this absorbtion, the attenuation of the waveguide is characterised by an attenuation coefficient « = . The relation between <- . and «_ * a is analogous to (8) : ^ _=-_ * v-.*F (12; Considering the relation (11) the laser diode according to the invention should work at *>C values between O.033 and 0.33 cm . Such low values are possible only due to low Pvalues and assuming that the free carri er absorbtion in the active region is the main loss mechanism. With these proposed values for c<- (0,033-0.33 cm ) and for F * ~4 -3 (1.5*10 -1.5*10 ) one should consider that for the high excitation of the active region, generating free carri ers in conduction and valence bands. the intrinsec absorbtion coefficient in the active region should not exceed 8 safety value ot apprαximateiy 200 cm . This value should be related with free carri er concentration in the active region necessary to obtain a sufficient gain to surpass losses. Total losses coefficient, due to mirror transmission and losses inside the cavity, «-< " + fft , nnaass aa vvaalluuee between 0.133 and 1.33 cm _ In st mulated emission conditions, total losses equal the modal wave gain 6 in the waveguide. So, G values are in the On . 3-1.33 cm nterval and considering P values in the 1.5*1'.. A -3 -1.5*10 interval , the intrinsec active region gain g a _=β/P should be approxi ately 89θ . Such ? value for the active region gain can be obtainec if the volume current density J v th D+ the threshold recombination current is in the order of magnitude 4 r> of 3*10 A/cm~Vpm and if, correspondingly, free carrier 18 — concentration is 2-3*10 cm " ' , what, corresponds to absorbtion coefficients of 40-60 cm , so that the mentioned value 200 cm is indeed a safety value. To obtain high e ficiencies, the volume current density J v should be few times greater than the volume current density at threshold, <-- v ttτ " * "ne increase in the volume current density J v is limited by the surface current density J s , the value of which determines the active region heating, and by the active region thickness by the relation: J v =J s /d a ( 13 ) J s maximum admissible values for the continuous, respectively quasicontinuous (0.2 ms, 100 Hz pulses) , regimes are 3 2 4 2 4*10 A/cm , respectively 10 A/cm . Smaller are the d a values, greater can be the J s values. The radiation flux obtained in an active region of length L, width w and thickness d a is: F= ( IvΛ/e- * -<3 s /d a~ J vth- * *w*d a *p/ ( o + ) U4 where k. represents the emitted photon energy and e the electron charge. The emitted flux should be to a safety factor s=2 smaller than the flux which produces catastrophic degradation and which is expressed by the formula (9). The optimum thickness of the active region can be determined from the formulae (9) and (14). Such optimum thicknesses of the active region are 0.045 pm and 0.11 um for the continuous, rspectively quasicontinuous, regimes —4 —3 for laser diodes with F =1.5*10 . For P =1.5*10 case, the optimum thicknesses of the active region are 0.11 pm, respectively 0.26 pm. For very short (100 nss pulse regime, the active layer thickness can be greater, but can not exceed 0.32 pm, as will be further shown. As shown by the relations (3) and (4; the active region thickness depends on the difference of refract ve indexes ng and m . The values of the refractive indexes n-. and n_=, are related to the corresponding energy band gap values of the semiconductor materials of the main region 3 and active region 5, and these values determine the emitted photon energies in the active region 5 and the band to band absorbtion coefficient for these photons in the main region 3. The n3 and ng values and the corresponding band gaps should be so that the mentioned absorbtion coe-fic ent is as small as possible, what means that the ma: r . region 3 is as transparent as possible for the radiation emitted in the active region. From this point of view it is prefered the main region to consists of an n type semiconductor and the energy gap of the main region 3 to be at least 120 meV greater than the energy of the emitted photons, to avoid band tail absorbtion. In the AlGaAε system to this energy difference corresponds a refractive index difference n -n3 equal to 0.07 and a maximum active region thickness equal to 0.32 pm. Also, the mam region 3 impurity doping should be kept to low concentration values to reduce free carrier losses and to avoid band tail absorbtion. Free carrier absorbtion in the main region should be smaller than 0.033 cm , respectively 0.33 cm , 16 and the free carrier concentration should be smaller than lo -3 1 _/ -3 cm " , respectively l cm " , for laser diodes with P equal to -4 -3 1.5*10 , respectively 1.5*10 " . To reduce tree carrier 17 absorbtion losses, the doping levels should be kept under 10 -3 cm in the intermediate region 4 and excitation region e>, too. A first example of laser diode according to the invention is a. structure in the AlGaAs system, with difterent values of the composition indexes and layer thicknesses. AlyGa j __ v As system is choosed to illustrate the invention since the material constants are better Iπown. All numerical examples above mentioned are related to this system, but other ternary and quaternary j j By and --■ii_-Vι compounds can as well be utilised using the same ideas: a structure with a separation layer between the active region and the main region of the waveguide, with a 2-5 pm wide main region, having the maximum of the radiation flux inside, with the radiation confined by a small difference between the limitation region and the main region refractive indexes, produced by a doping difference in tnε order of 10 cm " "' , with a radiation confinement factor n the order of 10 -2*10 ** and with a long resonator length of 1.5-3 cm. Can be used ternary compounds: Al.,Iπj__, ; P, Al ln j -.- s, Al >{ Gai_.,Sb, Al-,In 1 _--Sb, Ga x Inι_ -,P, Ga- j Inj- s, Ga : Inj__-,Sb, 6aP-,As j __-., GaAs x Sb j _ x , IπP- { Asι_ x , InAs--Sbι_-,; and quaternary: Al--Ga ; _ j; AsyP j _y, Al : ,G j _. ; SySbι_y, GawIni_- j PyAs j _y, Ga,,Inj_ As.,Sb j _y, (Al--Gaι_ ; -) in j _yP, (Al--Gaι_ ;, y In 1_ V S, (Al Ga _ m. y ) y In J—ySb , In (F'jjASj— ) ySb J_y . In the first example, a laser diode with a 2.3 cm resonator length and 1, respectively 0.62, mirror reflectivities is considered. The refractive indexes and the layers thicknesses are presented in tab. 1: Table 1 -4 The confinement factor ot this structure is 1.5*10 . Due to the relat vely high εtctive region thic. nesε th s structure is suitted for the quasicontinuous regime. " I he estimated total flux emitted without thr-- appearance of the catastrophic degradation is 3.8 1W per mm of the laser diode width in the p-n junction plane. The second example is a laser d ode wherein the main, intermediate and active region thicl-nesses are modified, according to tab. 2: Table 2 -4 The confinement factor of this structure is 1.5*10 , as in the previous example. The smaller active region thickness indicate this structure for the continuous regime. The total flux emitted without the appearance o-f the catastrophic degradation is 1.5 I- per mm of tne diode width n the p-n junction plane. The smaller- than in the first example value of the emitted flux is related to a smaller value for the active region thic. ness. The third example- refers also to a laser diode with a 2.3 cm Ienqth but with 1, respectively O.01, r flectivities. Such a diode can wort if the confinement factor is greater than in the previous cases, -f r e.,ε.mρle 1.5*10 "' . Refrεictive indexes and the layer thic. nesses are p'esented in tab. 3: fab1e 3 l yer 1 4 5 __ n- 3.522-7-<- 10 ~3 3.522 3.44C 3.590 3.440 T ^-x " ! " ^'' " ^ ~l 2 57ϊT 67TT >T y . 0. 097 0. 97 . 0. O U . 35 This diode is indicated for the contmous regime and the total flux emitted without the appearance of the catastrophic degrdration can be estimated to be o.38 I- per mm of the diode width in the p—n junction plane. The smaller flux compared to that of the second example structure is related to the nigher conf nemeπt factor P value. The forth example refers to laser diode wherein the main, intermediate and active region thicknesses are modified comparat vel y - to the previous examplε, according to the tab. 4: Table 4 This diode is indicated for the quasicontinuous reqi e. The flux emitted without the appearance of the catastrophic deqradation is aproximatelv 0.95 I- per mm o 4" the diode width in the p—n junction plane. The active region, with thicknesses from 0.045 to o.2__ pm can oe realised from succesive quantum wells, tor example quantum wells 7 n wide separated by 3 n wide barriers. If the wells with the mentioned width are made from GaAε and the barriers from Al j -Ga-j _ .-As with the composition index c=Q.23, then the energ> of the photons emitted from the active iaver is greater than the Oaήs oand gap and equal to 1.46.- eV in the particular considered case. The active region refractive inoex has tor this pnoton energy a mediated value r-, approxima el eq ε- tc 3.57. Tn& oand qap of the main region is 1.64 eV, 0.17 eV greeiter than th energy of the emitted photons. To this value of the photon energ corresponds a refractive index value equal to 3.53. Un the basis of an active region consisting of quantum wells, the fifths excimple is constructed, described in tab. 5s Table 5 y- 0.17 0.17 0.27 11 layers 0.0 0. 10 1avers 0.23 thicl-ness ratio 7/3 The confinement factor of this structure is 1.5*10 " . Since the active region consists of quantum wells the diode will wσrl with a reduced threshold current compared to that of the third example to which the diode has closed lεiyer thic. neεs and F coefficient values. The flux emitted without the appearance of the catastrophic degradati on is 0.38 tW/mm as in the third example. Structures without the intermediate region can be realised too in the frame of this invention. In such structures the band gap of the main region should be at least 20o meV greater than the active region band gap and the active region thicl-ness should be smaller than 0.25 p . When the active- region thickness is only 0.035 pm the confinement factor is 3.5*10 "' , respectively -4 1..-.-1G , 1 or structures with the main region thic. nesεes 2, respectively 5 pm. The laser diodes according tc the invention present the advantaqe that they work at hign densities o f the radiation fluxes and also _t high total flu?-, being constru tec -frorr simple structures with parallel between the two mirrors epitaxial layers.

Claims: Wfc CLAIM 1. A high power laser diode consisting ot a substrate (1) , a limitation region (2. , a main region (3) , an intermediate region (4) , an active recuon (5) , an excitation req on (6) and a contact region (7) , wherein the refractive index of the active region (5) is the highest n the structure, wherein the refractive index a- the main region (3) is the next interior one, wherein the product of the active region (5) thuclnesε by the square root of the difference of the squares of the refractive indexes of active (5) , respectively main regions (3) is smaller than a quarter o-f the vacuum wavelength of the laser radiation, wherein excitation .6) and intermediate (4) regions have conductivity types opposite to each other, in order to opperate at high radiation flux densities and to allow only the propagation of the fundamental transverse mode the maximum radiation flux ot which is located in the main region (3- and the effective refractive index of which is comprised between the retractive index values of the limitat n \ 2 < and o-t the main (3) regions, the product of the main region (3 1 thicl-ness by the square root of the difference of the squares of refractive indexes of the main (3) , respectively limitation (2) regions is smaller than half the vacuum wavelength o-f laser radiation, the difference between the refractive indexes ot the main (3; and limitation (2) regions is obtained onIs by di ferent doppiπg concentrations ot these regions, the diff rence +17 in earn p ** - concentrations being comprised between ?*lo and ■ + 1 "7 -3 0-9+-10 ' cm , correlated to the values for the main reqion .3- thicknes? between 2 and 5 pm, the confinement -factor is comprised —4 —3 between _.5*_0 and 1.5*10 and the resonator lenth is comprised between 1.5 and 3 cm. region (3) has n type conductivity and has the energy band gap at. least 0.12 eV greater than the energy of the photons emitted in the active region (5) and wherein the active region (5) thickness is maximum 0.32 pm. 3. A laser diode according to claims 1 and 2, wherein the main region (3) has a reduced doping level , under 10 cm ""' , 17 -3 respectively 10 cm , depending on the mentioned confinement factor values and the intermediate region (4) and the excitation region (6) have an impurity doping level under 10 cm " "' . 4. A laser diode according to claims 1.-.3, wherein the active region consists of quantum wells. (56) Bibliography: Great Britain Pattent 20311644 A.

Inventors: LAZANU SORINA, PETRESCU-PRAHOVA IULIAN BASARA, LAZANU, SORINA, PETRESCU-PRAHOVA, IULIAN, BASARAB
Applicants: INST DE FIZICA ATOMICA, INSTITUTUL DE FIZICA ATOMICA
Application year: 1991
Main classification: H01S3
IPC codes: H01L21, H01S5