BLUE AND DEEP BLUE LASER STRUCTURE LATTICE-MATCHED TO AN InP SUBSTRATE

Abstract: A II-VI semiconductor laser lattice-matched to an InP substrate. The differences in bandgap energies of adjacent layers are sufficiently large so that the resulting electrical and optical confinement provides a viable threshold current density. A p doped contact layer comprised of Zn, Te and Se may be lattice-matched to the structure; the inclusion of Te provides enhanced p doping. A buffer layer, in conjunction with a graded region, interposed between the substrate and the laser structure facilitates electron injection into the structure.

Description: Blue and deep blue laser structure lattice-matched to an InP substrate. BACKGROUND OF THE INVENTION This invention relates to semiconductor lasers and, in particular, to semiconductor injection lasers manufactured from π/NI materials and operating in the blue and deep blue region. Semiconductor lasers comprised of HI/V materials operating in the red and infrared regions are commonly found in optical data storage applications. Heterostructures (layer structures of materials of different energy band gaps) for HI/V materials are relatively easy to construct because certain m/N materials are inherently lattice matched. If laser devices operating at shorter wavelengths such as green, blue/green and blue were available, the data storage density of optical data storage devices could be increased. However, practical semiconductor laser diodes operating at the shorter wavelengths have proven more difficult to construct than the iπ/V structures referred to above. This is due, in part, to lattice mismatch, which causes strain at the interface of the layers, and makes good epitaxial growth difficult. The prior art has focused on a variety of means for utilizing II/VI materials with matched lattice constants to provide shorter wavelength semiconductor lasers. U.S. Patent No. 5,394,422 to Fitzpatrick ("Fitzpatrick") cogently describes some of the difficulties in constructing II- VI laser heterostructures that operate in the blue wavelength region. In order to attain higher band gaps, the various layers are usually made with elements from the right side of the periodic table. However, the addition of these smaller atoms to the compound typically serves to reduce the lattice constant of the compound, thus leading to mismatching. Inroads toward commercially viable II- VI blue lasers have focused on selecting particular compounds that will give sufficiently high band gaps (and, consequently, a lower threshold current density) along with layers that are lattice matched. This process is seen in U.S. Patent No. 5,363,395 to Gaines et al. Gaines et al. describe a blue-green π-VI (ZnSe) separate confinement heterostructure ("SCH") semiconductor injection laser. The SCH utilizes a Z^ ^ Cό^Se quantum well having Znj. -Mg-S y Se^ y cladding layers and ZnS z Se ι . z guiding layers on a GaAs substrate. The use of quaternary Zn^-Mg-S y Se^ cladding layers permits both lattice matching of all layers, and an increase of the cladding and guiding layer band-gaps. Thus, lasers can be made with improved electrical and optical confinement. The lattice constant of the GaAs substrate (which determines the lattice constant for the other layers) is 0.56537 nm. In the Gaines et al structure, the layers were lattice matched, for example, for u=0.2 in the active layer, z=0.06 for the guiding layer, and x=0.1 and y=0.1 for the cladding layer. For this particular cladding layer (Zn -9 Mg X S .jSe 9 ), the band gap of the cladding layer was approximately 2.95 eV. Such a structure can have a threshold current density on the order of 500 A/cm 2 for an output wavelength of approximately 516 nm at approximately 294°K. Fitzpatrick and Gaines et al. are incorporated into this specification by reference. One of the disadvantages of using the GaAs substrate for a ZnSe laser is that, as noted above, it has a relatively small lattice constant of approximately 0.56537 nm. Because the layers must be lattice matched to this relatively small lattice constant, it serves to constrain the differences in band gaps among the cladding, guiding and quantum well layers, thus increasing the lasing threshold current density. Fabrication of a contact layer with a GaAs substrate has also proven difficult. The lattice constant of ZnSe (0.56689 nm) is sufficiently close to GaAs to use as a contact layer. However, use of ZnSe as a p-type contact layer has been problematic because of the difficulty of doping ZnSe with a sufficiently high concentration of acceptors. (A doping concentration on the order of 10 18 cm '3 or higher is necessary.) More complex contact layers have been attempted. For example, alternating layers of ZnSe and ZnTe have been tried, because ZnTe is easier to dope p-type at higher concentrations. However, ZnTe has a relatively high lattice constant (0.6103 nm) relative to the nominal lattice constant of the structure (which can be considered the lattice constant of GaAs (0.56537 nm), the lattice constant of a ZnSe contact layer (0.56689 nm), or one of the other lattice matched layers). This difference between the lattice constant of the structure and ZnTe (approximately 8%) gives rise to strain and structural defects. Thus, the ZnTe must be used in small layers in order to reduce such structural defects. This highly refined contact layer has proven difficult to implement. SUMMARY OF THE INVENTION It is thus an objective of this invention to develop a laser heterostructure with a low threshold current density in the blue/deep blue spectral region. Accordingly, it is an objective of this invention to design a laser heterostructure with cladding and guide layers that have band gap differences that are large relative to each other, as well as to the quantum well. It is also an objective of this invention to design a laser heterostructure where such large differences in band gap energies between the layers are achieved while the layers remain sufficiently lattice matched to each other. In particular, it is an objective of this invention to design an SCH semiconductor injection laser comprised of Mg(ZnCd)Se layers on an InP substrate. The compositions of the quaternary layers of the laser are selected such that the layers remain lattice-matched to the InP substrate, while also ma taining the energy differences between each layer relatively high. Carrier and optical confinement is adequate to provide lasing in the blue and deep blue spectral regions at a viable threshold current density. Additionally, because of the higher lattice constant of InP (0.58688 nm) relative to GaAs, a ZnSeTe alloy contact layer may be lattice matched to the structure. The alloy will be highly p-type dopable. Alternatively, a p-type contact layer comprising alternating ZnSe-ZnTe layers would be better lattice matched to the structure: The lattice constants for the layers would differ from the structure by approximately 3.4% to 4.0%. Thus, the contact layer will have less structural defects than when ZnTe is used with a structure lattice matched to GaAs. In particular, the SCH semiconductor injection laser of the present invention includes a InP substrate having a lattice constant of approximately 0.58688 nm. The compositions of the layers are each in accordance with the formula Mg x (Zn y Cd 1-y ) 1-x Se. The values of x and y may be varied to select band gaps for the various layers between approximately 2.1 eV (for x=0, y=0.48) to approximately 3.6 eV (for x=0.9, y= l), while remaining lattice matched to the InP substrate. By selecting the compositions of the active layer, guiding layer and cladding layer such that the energy difference between each layer is approximately 0.3 eV, carrier and optical confinement is well maintained. Lasing at wavelengths in the blue and deep blue region (for example, at approximately 464 nm) with threshold current densities on the order of 400 A/cm 2 may be achieved. The InP substrate also provides a laser structure that supports a p-doped contact layer that has a sufficiently high carrier concentration and is either defect free or has acceptably small numbers of defects. The design of the SCH semiconductor injection laser of the present invention also includes alternating ZnSe-ZnTe contact layers or a composite ZnSeTe ternary layer lattice matched to InP. The invention also provides a solution for the relatively high energy discontinuity between the InP substrate and an adjacent n-type layer of the II- VI structure. Such an energy discontinuity impedes efficient injection of electrons from the substrate into the laser structure. The present invention overcomes this discontinuity by interposing at least one lattice-matched D3-V buffer layer between the InP substrate and the II- VI laser structure. The m-V layer has a conduction band energy level intermediate that of InP and the II- VI structure. Consequently, there are two energy discontinuities of reduced magnitude, which the injected electrons can overcome more efficiently. Additional refinements of this feature include providing "grading" between the InP substrate and the m-V buffer layer. Such grading can be accomplished, for example, through multiple intervening sub-layers of InP and the HI-V material interposed between the substrate and the DI-V buffer layer. By varying the thicknesses of the sub-layers a series of reduced energy discontinuities is established between the substrate and the buffer layer. BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention will be better understood and become readily apparent by referring to the following detailed description of an illustrative embodiment of a II- VI laser structure of the present invention, in conjunction with the accompanying drawings, in which: Fig. 1 is a graph of band gap versus lattice constant for compositions used in a π-VI structure in accordance with the present invention; Fig. 2 is one example of a sectional view of the layered structure of a 13- VI laser structure in accordance with the present invention; Fig. 3 is a plot of forward-biased band gap energy versus distance from the InP substrate for layers of the laser structure of Fig. 2; Fig. 4 is a plot of the calculated gain of a laser structure such as that shown in Fig. 2 versus wavelength of emission for three different doping levels; Fig. 5 is a plot of calculated laser output power as a function of the injected current of the structure such as that shown in Fig. 2, showing a threshold current density of approximately 400 A/cm 2 ; Fig. 6 is a plot of calculated threshold current density as a function of the amount of magnesium in the cladding layers of the structure such as that shown in Fig. 2; Fig. 7 is a plot of conduction band energy as a function of lattice constant for a number of materials; Fig. 8a shows the energy discontinuity between an InP substrate and an adjacent lattice-matched AlAS y Sbι. y layer; Fig. 8b shows a graded energy region interposed between the InP substrate and an adjacent lattice-matched AlAS y Sbι. y layer of Fig. 8a; Fig. 9 shows a particular embodiment of a graded energy region between an InP substrate and a lattice-matched AlAS y Sb 1-y buffer layer; and Fig. 10 shows a π-VI laser diode structure of the present invention with an InP substrate and an interposed AlAS y Sb^ y buffer layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in Fig. 1, substrate InP has a lattice constant of approximately 0.58688 nm. Also shown in Fig. 1 are three binary compounds: ZnSe, having a lattice constant of 0.56689 nm and energy band gap of 2.67 eV (at 300°K); CdSe, having a lattice constant of 0.6084 nm and energy band gap of 1.70 eV (at 300°K); and MgSe, having a lattice constant of approximately 0.588 nm and energy bandgap of approximately 4.0 eV (at 300°K). (Unless otherwise noted, all of the following references to bandgap energy will be for 300°K.) The compositions of the layers of the SCH semiconductor laser generally correspond to the formula: Mg x (Zn y Cd 1-y ) 1 . x Se (Eq. 1) where x and y are chosen such that 0_<.x_<.l and 0_≤.y_<.l. It is seen that the band gap energies and lattice constants for layers having compositions according to Eq. 1 fall within (or along the border of) the shaded triangle 10. Moreover, for the layers to be lattice matched to the InP substrate, they must be chosen from the compounds within (or at the border of) triangle 10 that have a lattice constant of 0.58688 nm. This is shown by the vertical line bisecting triangle 10 between reference points A and B. It is seen from Fig. 1 that point A corresponds to the compound with the lowest band gap described by Eq. 1 and lattice matched to InP. This lower energy limit compound is Zn 04g Cd 052 Se (i.e., x=0; y=0.48 in Eq. 1), having an energy band gap of 2.10 eV. Similarly, point B corresponds to the compound with the highest bandgap energy described by equation 1 and lattice matched to InP. This upper energy limit compound is Mgo.gZr- d Se (i.e., x=0.4; y=l in Eq. 1), having an energy bandgap of 3.60 eV. Fig. 2 illustrates a preferred embodiment of the structure of the invention. The structure includes an InP substrate 20. A lower cladding layer 22 is grown on substrate 20. Grown atop lower cladding layer 22 is lower guide layer 24. Active quantum well layer 26 is grown atop lower guide layer 24. Upper guide layer 28 is grown atop active layer 26, and upper cladding layer 30 is grown atop upper guide layer 28. Finally, contact layer 32 is grown atop upper cladding layer 30. The lower layers are n-type doped, and the upper layers are p-type doped. In a preferred exemplary embodiment of the structure of the present invention, for lasing at 2.67 eV (464 nm), the lower and upper cladding layers 22, 30 are constructed of Mg 072 (Zn 089 Cd 0 . n ) 0.2g Se (corresponding to x=0.72, y=0.89 in Eq. 1) and are each approximately lm thick. The lower cladding layer 22 is Cl-doped with a concentration of 2xl0 17 cm "3 , and the upper cladding layer 30 is N-doped with a concentration of lxlO^m " 3 . (In general, once x is defined for Eq. 1, and the lattice constant to be matched is selected, the value of y may be calculated. Thus, when x is given, particular values for y may not be referred to, for example, as in Fig. 2.) The lower and upper guiding layers 24, 28 are constructed of Mg 054 (Zn 078 Cdo. 22 )o. 46 Se (corresponding to x=0.54, y=0.78 in Eq. 1) and are each approximately 100 nm thick. The lower and upper guiding layers 24,28 are Cl- and N-doped, respectively, both with concentrations of lxl0 17 cm" 3 . The active quantum layer is constructed of Mg 034 (Zn 065 Cdo .35 )o. 66 Se (corresponding to x=0.34, y=0.65 in Eq. 1) and is approximately 6 nm thick. Either a p-type ZnSe-ZnTe or a p-type ZnSeTe ternary alloy contact layer 32 is grown atop upper cladding layer 30. Referring back to Fig. 1, it is seen that the lattice constant of InP (0.58688 nm) is larger than both GaAs (0.56537 nm) and ZnSe (0.5668 nm), but less than ZnTe (0.6103 nm). Thus, a composite ternary alloy ZnSeTe may be grown atop upper cladding layer 30 that is lattice matched to the InP and contains a sufficiently high concentration of acceptors. The composition of the ternary alloy may be, for example, approximately 50% ZnSe and 50% ZnTe. The ternary layer is approximately 100 nm thick and is N-doped with concentration of lxl0 18 cm "3 . Alternatively, the contact layer 32 may be a graded composite of alternating layers of ZnSe and ZnTe. As noted above, the lattice constant of the InP based structure is nominally 0.58688 nm. This is approximately midway between the lattice constants of ZnSe and ZnTe; thus, the lattice mismatch of a layer of ZnSe is approximately 3.4% and the lattice mismatch of a layer of ZnTe is approximately 4.0%. (Such levels of mismatch are superior to growing a ZnTe layer on a GaAs structure where, as noted above, the mismatch will be approximately 8%.) The layer thickness of ZnSe is varied from 1.8 nm to 0.2 nm, decreasing 0.1 nm per layer; the layer tickness of ZnTe is varied from 0.2 nm to 1.8 nm, increasing 0.1 nm per layer. The overall number of layers may be approximately 34 nm thick. The ZnSe layers are N-doped with a concentration of approximately 10 18 cm "3 , and the ZnTe layers are N-doped with concentration of lxl0 19 cm "3 . As described in more detail below, this particular structure will have a threshold current density on the order of 400 A/cm 2 and peak wavelength of approximately 464 nm. Experimental Results Simulations were developed to explore the performance of the Mg x (Zn y Cd ι-y ) 1 . x Se-based quantum well laser, in particular, the laser structure shown in Fig. 2 having the dimensions and compositions described above. Other parameters pertinent to the simulation were first developed and/or modeled for the structure: Fig. 3 shows band gap energies of the various layers of the structure shown in Fig. 2 as a function of distance relative to the quantum well 26. Fig. 3 was constructed using the dimensions and compositions of the structure given above with respect to Fig. 2 and the band-gap energies shown in Fig. 1. It is known in the art that the conduction band offset ratio (QJ at the layer interfaces is a particularly important parameter for the performance of the laser. is the ratio of the change the conduction band energy to the change in the overall bandgap energy at an interface. (The change in overall bandgap energy at the interface is equivalent to the sum of the change in conduction band energy and the change in valence band energy.) Thus, referring to Fig. 3, for example, Q. for the interface between guide layer 24 and quantum well 26 is AE C ΔE ' c +Δ —E " v Conduction band offset ratios have been deterrnined experimentally to be approximately 0.6 for a MgSe/Cd 0.54 Zr -046 Se system. Because of the similarities in the physical properties to the present system, 0.6 for the conduction band offset ratios (Q at the quantum well/guide and guide/cladding interfaces. The compositions chosen for the layers give bandgaps that are each separated by approximately 0.3 eV. Thus, lower and upper cladding regions 22, 30 have energy band gap of approximately 3.3 eV, lower and upper guide layers 24,28 have energy band gap of approximately 3.0 eV, and active layer 26 has an energy band gap of approximately 2.67 eV. A generalized equation for the index of refraction (nt) of a quaternary layer containing Mg, as described by Eq. 1, is known. For the particular quaternary layers with compositions described above with respect to Fig. 2, and having band gaps given directly above, the indices of refraction are: Cladding layers Mg 072 (Zn y Cd ι-y ) 0 . 28 Se: nj = 2.483 Guiding layers Mg 054 (Zn y Cd 1 . y )o. 46 Se: fy = 2.682 Quantum Well Mg 0.34 (Zn y Cd 1-y )o. 66 Se: ^ = 2.707 The simulation model applied to the laser structure of Fig. 2, as further described by the parameters developed above, used a theoretical model for lasers based on self-consistent solutions of drift-diffusion and optical equations. Kp theory was used to account for strained (or unstrained) quantum well active layers. A gain broadening model accounted for broadening due to carrier-carrier scattering and using r,^ = 30fs. The effective masses of electrons and holes used for each of the layers were set equal to those for ZnSe. Electron and hole mobilities of 100 cm 2 /Vs and 7 cm 2 /Vs were selected (comparable to used for MgZnSSe layers in blue-green ZnCdSe-based SCH lasers). Minority carrier lifetime in undoped guiding layers was set at 2ns, the same as the experimental value for undoped ZnSe. Simulation results for the structure are given in Figs. 4 and 5. In Fig. 4, the gain is given for various injection levels into the active region. For carrier concentrations on the order of lxlO l9 cm" 3 , a positive gain is observed around peak wavelength of approximately 464 nm, corresponding to the transition energy between n= l electron and heavy-hole sub-bands. As shown in Fig. 5, this corresponds to a threshold current density of approximately 400 A/cm 2 for the structure. (The current, approximately 4mA, divided by the area of the structure, 1000 square microns.) The threshold is lower than that predicted for blue/green lasers based on ZnCdSe/ZnSSe/ZnMgSSe SCH structures, which is on the order of 500 A/cm 2 at room temperature. The difference is attributed to the heightened optical confinement attained by optimizing the difference in band-gap between the guiding and cladding layers. For blue/green lasers based on ZnCdSe/ZnSSe/ZnMgSSe, the difference in band-gap between the guiding and cladding layers is only 139 meV; thus, the difference in the indices of refraction is only 0.084. For the Mg x (Zn y Cd 1 . y ) 1 . x Se-based quantum well laser described above, however, the difference in band-gap between the guiding and cladding layers is selected to be approximately 300 meV; the difference in the indices of refraction is 0.199. The importance of the difference in band-gap between the cladding and guiding layers for optical confinement was underscored by manipulating the Mg in the cladding quaternary layer in the simulation. Fig. 6 shows that the threshold current density increases markedly as the percentage of Mg in the cladding quaternary layer is reduced. By reducing the percentage of magnesium in the cladding layer, the difference in band gap (and, thus, the difference in the indices of refraction) between the cladding and guiding layers is reduced. This reduces the optical confinement, thereby increasing the threshold current density, as shown in Fig. 6. The interface between the InP substrate and the π VI laser structures of the present invention can present difficulties. As noted above with respect to Fig. 4, the injected current into the active region must be sufficiently high for there to be a positive gain. Accordingly, a sufficient number of electrons must be injected from the n-type substrate into the n-doped compound. For the structure of Fig. 2 described above, electrons flow from the InP substrate 20 to the adjacent lower cladding layer 22. Referring to Fig. 7, it is seen that the discontinuity between the conduction band energy of InP and a lattice matched TL/Y compound (taken, for example, in Fig. 7 to be the difference X between InP and ZnSe) is nominally 0.8 eV. This discontinuity can be too high to generate sufficient carrier density when the II- VI "compound" is a layer, such as the n-type cladding layer, of the laser structure of the present invention. The magnitude of this discontinuity may be reduced by interposing at least one m-V layer between the InP substrate and II- VI structure. The m-V layer has conduction band energy intermediate that of InP and the adjacent π-VI material. Thus, the m-V interposed layer can create two energy discontinuities of reduced-magnitude that can be overcome more readily by the injected electrons. For example, referring again to Fig. 7, the discontinuity between the conduction band energy of lattice-matched (or pseudomorphic) m-V material AlAS y Sbι. y and a lattice-matched (or pseudomorphic) π/VI compound is approximately 0.2 eV. (This is shown as the difference Y in conduction band energy between AlAS y Sb^ y and ZnSe in Fig. 7; AlAS y Sb 1-y is lattice-matched or pseudomorphic to InP when y is approximately 0.56, or AlAs 0 . 56 Sbo . .) The exact energy barrier is also a function of the doping level of the AlAS y Sb^ y buffer layer and adjacent layer of the π VI structure; however, with this lower barrier to overcome, the injection of electrons from the AL S y Sbj. y layer into the adjacent II- VI structure would be much more efficient. It is known in the art that such a lattice-matched AlAS y Sb 1-y layer may be grown atop an InP substrate. (Such layers have been used to reduce defects.) Accordingly, injection of electrons from such a A]As y Sb 1-y layer into an adjacent π/VI structure will be much more efficient. However, Fig. 7 shows that the discontinuity between the conduction band energy of the InP substrate and lattice-matched AlAS y Sbi. y is approximately 0.6 eV. (This is shown as the difference Z in Fig. 7.) In general, this energy discontinuity between the InP substrate and the m-V buffer layer is still relatively high a barrier for providing direct injection from the substrate into the lattice-matched buffer layer. Thus, it is desirable to provide a "graded" region where the energy transitions from the level of the InP substrate to the energy level of the m-V buffer layer. Fig. 8b is an energy diagram depicting such a "graded" region for the particular example above, between the InP substrate and the AlAS y Sb,^ buffer layer. Fig. 8a is an energy diagram of a discontinuous change, where there is no grading. In both cases, injected electrons must overcome a 0.6 eV barrier, but they will pass through a 0.6 eV graded barrier much easier than a discontinuous one. Such grading may be accomplished in general by applying alternating sub- layers of InP and the m-V material onto the InP substrate, increasing the thickness of successive m-V sub-layers while reducing the thickness of successive InP sub-layers. With this series of sub-layers, the discontinuity between the substrate and the m-V buffer layer can be reduced to a series of small discontinuities spread out over a distance, thus approaching a continuous energy transition. In the particular example developed above, such grading may be accomplished by interposing a series of alternating InP and AlAS y Sbj. y sub-layers with variable thicknesses between the InP substrate and the AlAS y Sbj. y buffer layer. Fig. 9 shows an example of such a "digitally graded" region providing the energy transition between the InP and the AlAS y Sb^ y layer. As shown, the sub-layer 102 of AlAS y Sb 1-y directly adjacent the substrate InP may be approximately 0.5 nm, and the next sub-layer 104 of InP is approximately 2.5 nm. Successive sub-layers of ALAS y Sb Ly are increased by 0.1 nm, while successive sub-layers of InP are decreased by 0.1 nm. The sub-layer of AlAS y Sb^ y 182 closest the AlAS y Sbi. y layer is 2.5 nm, and the sub-layer of InP 184 adjacent the AlAS y Sb 1-y layer is 0.5 nm. Addition of all InP and AlAS y Sb 1-y sub-layers (forty two in all) shows that the graded region is approximately 63 nm for the 0.6 eV change in energy. (The grading should provide for approximately 10 nm per 0.1 eV.) per 100.) Such digital grading will approximate the graded 0.6 eV transition in energy between InP and AlAS y Sbι -y shown in Fig. 8b. Alternatively, the graded region may be an alloy of In, P, Al, As and Sb with a continuous change in composition in the graded region. The composition of the alloy in the region directly adjacent the substrate would be 100% InP (i.e., no Al, As and Sb), and the alloy in the region directly adjacent the AlAS y Sb^ buffer layer would be 100% AlAS y Sbi. y . Moving through the graded region away from the substrate, the percentage of InP in the alloy would decrease from 100% to zero, and the percentage of AlAS y Sbι_ y would increase from zero to 100%. Fig. 10 shows that the discontinuity between the substrate and the ALAS y Sbj. y may alternatively be circumvented altogether. By applying a contact directly to the ALAs y Sb 1-y buffer layer to the side of the II- VI structure, electrons are injected directly into the buffer layer and, from there, into the UNI structure. Thus, there is no need for a graded region between the substrate and the buffer layer, because the electrons do not pass through it. It will be understood that various modifications can be made to the various embodiments of the present invention herein disclosed without departing from its spirit and scope. As noted above, for example, various compositions of the layers are contemplated. Also, there are a wide range of choices of the 13/ VI elements that can be used in the layers that make up the laser structure. All combinations would fall within the scope of the present invention. Therefore the above description of a preferred example of the structure should not be construed as limiting the invention but merely as presenting preferred embodiments of the invention. Those skilled in the art will envision other modifications within the spirit and scope of the present invention as defined by the claims presented below.

Claims: CLAIMS: 1. A semiconductor laser comprised of II- VI layers of compounds with elements selected from the group of Mg, Zn, Cd and Se, said layers lattice-matched to an InP substrate. 2. A semiconductor laser as in Claim 1, wherein the II- VI layers include a quantum well, p and n doped guiding layers, and p and n doped cladding layers. 3. A semiconductor laser as in Claim 2, wherein the compositions of the layers are each in accordance with the formula 4. A semiconductor laser as in Claim 2, wherein the composition of the quantum well layer is substantially in accordance with the formula wherein the composition of the cladding layers are substantially in accordance with the formula Mg 0 . 72 (Zno. 89 Cd 0 . 1 ι)o. 28 Se and wherein the composition of the guide layers are substantially in accordance with the formula Mgo . 5 (Zn 078 Cd 0 . 22 )o. 46 Se. 5. A semiconductor laser as in any of the preceding Claims, further comprising a p doped contact layer that is pseudomorphic to the laser structure, is comprised of Zn, Se and Te and preferably is comprised of an alloy of approximately 50% ZnSe and approximately 50% ZnTe. 6. A semiconductor laser as in any of the preceding Claims, wherein at least one of the 13- VI layers is lattice matched to the InP substrate. 7. A semiconductor laser as in any of the preceding Claims, wherein a pseudomorphic m-V buffer layer interposed between the substrate and the laser structure, a graded region between the substrate and the buffer layer providing at least one intermediate level of conduction band energy between the substrate and the buffer layer. 8. A semiconductor laser as in Claim 7, wherein the graded region is comprised of a number of alternating sublayers of InP and the material of the m-V buffer layer. 9. A semiconductor laser as in Claim 7 or 8, wherein the buffer layer is comprised of Al, As and Sb. 10. A semiconductor laser as in Claim 9, wherein the buffer layer is substantially in accordance with the formula AlAso. 56 Sb 44 .

Inventors: SHAHZAD KALID, SNOEKS EDWIN, SHAHZAD, KALID, SNOEKS, EDWIN
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1998
Main classification: H01L33
IPC codes: H01L33, H01S5