Abstract:
A method for making high quality InGaAsN semiconductor devices is presented. The method allows the making of high quality InGaAsN semiconductor devices using a single MOCVD reactor while avoiding aluminum contamination.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application relates to the co-pending application Ser. No. 10/106,678, filed on the same day, entitled “Asymmetric InGaAsN Vertical Cavity Surface Emitting Lasers” by Takeuchi, Chang, Bour, Leary and Tan, owned by the assignee of this application and incorporated herein by reference. 
    
    
     BACKGROUND 
     The invention relates to a method for making high quality InGaAsN semiconductor devices using metal organic chemical vapor deposition. 
     InGaAsN is an attractive material for a variety of semiconductor applications. InGaAsN is useful in the area of long wavelength edge-emitting lasers and vertical cavity surface emitting lasers (VCSEL) in the optical communications area because the material is readily grown on GaAs wafers which provides higher conduction band offset and allows the use of GaAs/AlAs high reflective distributed Bragg reflectors (DBRs). 
     A number of research groups have achieved room temperature continuous wave (CW) operation of InGaAsN VCSELs that were made using molecular beam epitaxy (MBE). Room temperature continuous wave operation of InGaAsN VCSELs has been achieved in VCSELs made using metal organic chemical vapor deposition (MOCVD) using dimethylhydrazine (DMHy) as a source of nitrogen. MOCVD is preferred over MBE as the growth technique for achieving mass production. To achieve commercial use of InGaAsN VCSELs, further improvements in device performance such as lowering the threshold current density and extending the device lifetime are necessary. 
     It has been reported by Sato et al. in Electronics Letters, 33, 1997, 1386, that the surface morphology of the InGaAsN active region grown directly on the AlGaAs cladding layer using MOCVD appears powder-like, indicating three dimensional growth. Kawaguchi et al. report in Electronics Letters 36, 2000, 1776, that continuous MOCVD growth of InGaAsN layers on GaAs/AlGaAs layers results in poor optical quality of the InGaAsN layer while switching to a two reactor process yields a substantially better optical quality InGaAsN layer. Sato et al., IEEE Photonics Technology Letters, 12, 1999, 1386 achieved good results for a highly strained GaInAsN ridge stripe laser using MOCVD by using aluminum free cladding layers. This approach is not useful for VCSELs because the highly reflective AlGaAs/GaAs DBR mirror can not be used. 
     SUMMARY OF THE INVENTION 
     Investigation by secondary ion mass spectroscopy (SIMS) indicates that conventional metal organic chemical vapor deposition (MOCVD) growth of InGaAsN active layers on GaAs/AlGaAs layers results in appreciable aluminum contamination (close to one percent) and is responsible for performance loss in a variety of semiconductor devices. Poor optical properties of InGaAsN active regions for InGaAsN edge emitters and InGaAsN VCSELs as well as lower than expected current gain in bipolar transistors are attributable to Al contamination of the active regions. In InGaAsN solar cell and InGaAsN photodetector structures (see for example, R. R. King et al, Conference Record of the 28 th  IEEE Photovoltaic Specialists Conference, 2000, 998 and J. B. Heroux et al, Applied Physics Letters, 75, 1999, 2716), elimination of Al contamination results in high quality InGaAsN absorbing layers that result in higher quantum efficiencies for those semiconductor devices. Additionally, InGaAsN active regions grown over AlGaAs layers show more O and C incorporation than InGaAsN active regions grown without underlying AlGaAs layers. To avoid aluminum incorporation into InGaAsN layers, embodiments in accordance with the invention are disclosed. 
     In accordance with the invention, either layers are grown in the semiconductor structure whose growth serves to getter Al atoms/Al containing molecules or chemicals may be introduced into the MOCVD chamber via flow gases that serve to getter Al atoms/Al containing molecules. The methods reduce the Al content that is incorporated into the N containing layers and result in improvements in the quality of the InGaAsN layer including smoother surface structure, improved optical qualities and lower levels of recombination centers due to, for example, O and C incorporation that typically accompanies the Al incorporation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  shows a side view of a typical MOCVD reactor in accordance with the invention. 
     FIG. 1 b  shows a top view of a typical MOCVD reactor in accordance with the invention. 
     FIG. 2 shows arrangement of the chemical delivery system for the typical MOCVD reactor in FIG. 1 a  and FIG. 1 b    
     FIG. 3 shows a test structure in accordance with the invention. 
     FIG. 4 shows a test structure in accordance with the invention. 
     FIG. 5 shows an edge emitting laser structure in accordance with the invention. 
     FIG. 6 shows a vertical cavity surface emitting laser structure in accordance with the invention. 
     FIG. 7 shows a hetero bipolar transistor structure in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the invention, methods are disclosed to control incorporation of Al from the growth of Al containing layers such as AlGaAs layers into active InGaAsN layers that are grown continuously on GaAs/AlGaAs. These methods typically involve either the growth of layers in the semiconductor device that serves to getter Al atoms/Al containing molecules or the introduction of chemicals into the MOCVD chamber with flow gases that serve to getter Al atoms/Al containing molecules without accompanying layer growth. 
     In accordance with the invention, layers whose growth also functions to getter Al atoms or molecules containing Al can be grown at any time before the growth of the InGaAsN layer or between growth of the InGaAsN active layer and the previously grown AlGaAs layer to reduce Al contamination of the InGaAsN active layer. Typically, layers whose growth involves atoms/molecules which react more effectively with Al or Al containing molecules than As atoms or molecules containing As are suitable. In particular, growth of layers that contain N and/or P atoms is typically effective in reducing the Al contamination when the total amount of N and/or P atoms introduced into the MOCVD reactor is greater than the amount of Al atoms that are introduced into the MOCVD reactor prior to the growth of the InGaAsN active layer. Hence, the absolute amounts will be MOCVD reactor specific. The flow rate of the Al gettering chemical and time of application is determined by setting the total amount of gettering atoms such as N and/or P introduced by the flow to be greater than the total amount of Al introduced into the reactor chamber. It should be noted that in accordance with the invention it is effective to use this method even if Al layers in the device structure are only grown after the InGaAsN active layer is grown since in commercial applications, reactors are used repeatedly to grow the same device structure leading to Al contamination from the previous run. 
     In accordance with the invention, chemicals that getter Al atoms/Al containing molecules may be introduced via flow gases into the MOCVD reactor anytime before growth of the InGaAsN layer or anytime before growth of the InGaAsN layer and after growth of the AlGaAs layer to reduce Al contamination of the InGaAsN layer. Typically, chemicals that can react more effectively with Al atoms/Al containing molecules than As atoms or molecules containing As are introduced via flow gases into the MOCVD reactor anytime before growing the InGaAsN layer or anytime before growth of the InGaAsN layer and after the growth of the AlGaAs layer. In particular, introduction of chemicals that contain N and/or P atoms via flow gases into the MOCVD is typically effective when the total amount of N and/or P atoms in the chemicals is greater than the total number of Al atoms that are introduced before the InGasAsN layer is grown. 
     In accordance with the invention, any semiconductor devices using InGaAsN layers and Al containing layers such as AlGaAs, AlGaInP and AlGaInAsP may be made using a single reactor MOCVD process while obtaining high quality InGaAsN layers having low levels of Al contamination. For example, solar cell and photodetector device structure using high quality InGaAsN absorbing layers results in higher quantum efficiencies while bipolar transistors using InGaAsN collector and base layers suffer less from the presence of recombination centers which lead to low current gain. 
     In accordance with the invention, FIG. 1 a  shows MOCVD reactor  120  in side view with exhaust line  180 . MOCVD reactor  120  is a cold wall, quartz reactor. Group-III source injection occurs at inlet  125  and Group-V source injection occurs at inlet  130 . Group III and Group V gases begin mixing after passing from outlets  187  and  188 . Outlets  187  and  188  are both approximately 13 cm×2 cm rectangles. Vertical height  143  of MOCVD reactor  120  is approximately 4.5 cm while dimension  144  is approximately 3 cm. Dimension  148  is approximately 7 cm and is the distance from where the Group III and Group V gases begin to mix to where the vertical constriction of MOCVD reactor  120  starts. Dimension  147  is approximately 7 cm and SiC-coated graphite susceptor  170  has diameter  146  of approximately 11 cm with thickness  145  of approximately 1.5 cm. Substrate  175  is positioned on susceptor  170  as shown in FIGS. 1 a  and  1   b . With reference to FIG. 1 b , lateral dimension  185  of MOCVD reactor  120  is approximately 13 cm while dimension  149  is approximately 1.5 cm. 
     In accordance with the invention, FIG. 2 shows an arrangement of the chemicals and lines feeding into MOCVD reactor  120 . MOCVD reactor  120  is typically a cold wall, quartz reactor. Valves  250 ,  251 ,  252  and  253  control and direct flow from tanks  231 ,  232 ,  233 , and  234 , respectively. Valves  254 ,  255 ,  256 ,  257 ,  258 ,  259  and  260  control and direct flow from bubblers  235 ,  236 ,  237 ,  238 ,  239 ,  240  and  241 , respectively. Inlet  210  serves to introduce H 2  carrier gas into MOCVD reactor  120  via line  212  to inlet  130  of MOCVD reactor  120 . Line  212  serves as well for typically introducing Tertiarybutylarsine (TBAs) from bubbler  235  and Dimethylhydrazine (DMHy) from bubbler  236  into MOCVD reactor  120  via inlet  130 . Valves  254  and  255  direct flow from bubblers  235  and  236 , respectively, into either line  212  or vent line  220 . Vent lines  220  connect to exhaust line  180 . Line  221  serves to introduce H 2  into bubblers  235  and  236  while line  222  serves to introduce H 2  into bubblers  237 ,  238 ,  239 ,  240  and  241 . Line  211  serves to introduce NH 3  from tank  231 , AsH 3  from tank  232 , PH 3  from tank  233  and Si 2 H 6  from tank  234  into MOVCD reactor  120  via inlet  130 . 
     Valves  250 ,  251 ,  252  and  253  direct flow from tanks  231 ,  232 ,  233  and  234 , respectively, into either line  211  or vent line  220 . Line  213  serves to typically introduce Trimethylgalium (TMGa) from bubbler  237 , Triethylgallium (TEGa) from bubbler  238 , Trimethyaluminum (TMAl) from bubbler  239 , Trimethylindium (TMIn) from bubbler  240  and CBr 4  from bubbler  241  into MOCVD reactor  120  via inlet  125 . Valves  256 ,  257 ,  258 ,  259  and  260  direct flow from bubblers  237 ,  238 ,  239 ,  240  and  241 , respectively, into either line  213  or vent line  220 . Note that there is no back flow in any of the lines since a mechanical pump (not shown) maintains the pressure inside reactor  120  at about 100 mbar. 
     FIG. 3 shows InGaAsN quantum well photoluminescence (PL) test structure  300  in an embodiment according to the invention. To grow test structure  300 , GaAs buffer layer  325 , typically having a thickness in the range of about 1000-5000 Å, is grown on GaAs substrate  320  at a temperature in the range of about 600-800° C. using Trimethylgallium (TMGa) and arsine (AsH 3 ) at a pressure in the range of about 50-400 mbar H 2  ambient. Then Al 0.3 Ga 0.7 As layer  330 , typically having a thickness of 0.9 μm, is grown on GaAs buffer layer  325  by introducing Trimethylaluminum (TMAl). The introduction of TMAl is then stopped and GaAs layer  335  is grown to a thickness in the range of about 50-300 Å. The total amount of TMAl supplied is about 4×10 −4  mol. Following growth of GaAs layer  335 , the growth process is interrupted by shutting off the supply of TMGa. A flow of AsH 3  typically at about 300 sccm is continuously introduced into an MOCVD reactor such as MOCVD reactor  120  to prevent degradation of the exposed surface of GaAs layer  335 . Surface degradation is typically a problem if the temperature exceeds approximately 400° C. and should be avoided. 
     Then, typically, NH 3  (ammonia) is introduced at a typical flow rate of about 500 sccm at a temperature and pressure in the range of about 400-700° C. and 50-1000 mbar, typically at 500-600° C. and 100 mbar, respectively. NH 3  is attractive for reasons of cost and purity. The application time for the NH 3  can be varied, typically from between about 0.5 minutes to about 4 minutes. Longer application times reduce the amount of ambient Al available for incorporation into InGaAsN layer  350  and InGaAsN layer  360 . An application time of 0.5 minutes at a flow rate of about 500 sccm introduces about 1×10 −2  mol of N atoms while an application time of about 4 minutes at a flow rate of about 500 sccm introduces about 8×10 −2  mol of N atoms into MOCVD reactor  120 . The amount of N atoms introduced changes linearly with the time of application. The selected time and flow rate of the NH 3  assure that the total number of N atoms is greater than the total number of Al atoms introduced into MOCVD reactor  120  prior to InGaAsN growth. In accordance with an embodiment of the invention, NH 3  strongly reacts with TMAl, the Al source used in the growth of the Al containing layers, even at room temperature. NH 3  also has a very high pyrolysis temperature in comparison to the growth temperature of GaAs based material so that undesired incorporation of N into the surface of GaAs layers is minimized during the NH 3  flow. NH 3  is also attractive for reasons of cost and purity. NH 3  may be replaced by a number of other chemicals which contain nitrogen atoms or phosphorus atoms and react strongly with Al sources to fulfill the Al gettering function, such as, for example, Monomethylamine, Dimethylamine, hydrazine, Monomethylhydrazine, Dimethylhydrazine, Tertiarybutylhydrazine, Phenylhydrazine, phosphine or Tertiarybutylphosphine. In general, chemicals that react strongly with Al sources to fulfill the Al gettering function may be used as long as the chemicals do not have a strong adverse effect on the semiconductor layers. 
     Following the NH 3  flow, growth is resumed with GaAs layer  336 . GaAs wave guide layer  336  is grown to a thickness in the range of about 1000-2000 Å as the temperature is decreased to about 500-600° C. Following completion of the growth for GaAs layer  336 , InGaAsN active layer  350  is grown to a thickness in the range of about 60-100 Å at a temperature in the range of about 500-600° C. using Triethylgallium (TEGa), Trimethylindium (TMIn), Tertiarybutylarsine (TBAs) and Dimethylhydrazine (DMHy). The ratio of DMHy/(DMHy+TBAs) in the range of 0.95-0.99 is used for growth of InGaAsN active layers  350  and  360 . GaAs barrier layer  355  is inserted between InGaAsN active layer  350  and InGaAsN active layer  360 , having a thickness in the range of about 100-300 Å. Then InGaAsN active layer  360  is grown to a thickness in the range of about 60-100 Å at a temperature in the range of about 500-600° C. using Triethylgallium (TEGa), Trimethylindium (TMIn), Tertiarybutylarsine (TBAs) and Dimethylhydrazine (DMHy). After growth of InGaAsN active layer  360 , GaAs wave guide layer  370  is grown to a thickness in the range of about 1000-2000 Å while the temperature is increased to about 600-800° C. and using Trimethylgallium (TMGa) and arsine (AsH 3 ) at a pressure in the range of about 50-1000 mbar H 2  ambient. Then Al 0.3 Ga 0.7 As layer  380  is grown, by introducing TMAl, to a thickness in the range of about 1000-2000 Å and growth is completed with GaAs cap layer  390  grown to a thickness which is in the range of about 50-300 Å. 
     Another embodiment in accordance with the invention is shown in FIG.  4 . Test structure  400  is similar to test structure  300  but test structure  400  adds GaAsN non-active layer  450  having a typical thickness of about 600 Å after growth of GaAs layer  335 . GaAsP may be substituted for GaAsN in non-active layer  450 . GaAs layer  335  is deposited as described above. Then GaAsN non-active layer  450  is grown by introducing TMGa and AsH 3  at a flow rate of typically about 300 sccm continuously and NH 3  at a flow rate of typically about 500 sccm for approximately 4 minutes while decreasing the growth temperature to a range of 500-600° C. Next GaAs layer  436  is grown to a thickness in the range of about 400-1000 Å before growing InGaAsN active layer  350  as described above. The selected time and flow rate of the NH 3  assure that the total number of N atoms is greater than the total number of Al atoms introduced into reactor  120  prior to InGaAsN growth. All subsequent steps are as previously described for test structure  300 . 
     In the event that InGaP is substituted for GaAsN in non-active layer, TMGa, Trimethylindium (TMIn) and PH 3  at a flow rate of 500 sccm are supplied in place of TMGa and AsH 3 . Typical thickness is still about 600 Å. The temperature is typically kept at about 700° C. for the InGaP growth. After completion of the InGaP growth, TMGa and AsH 3  are supplied for growing GaAs layer  436  having a thickness in the range of about 400-1000 Å while the temperature is typically decreased to a range of about 500-600° C. for growth of InGaAsN active layer  350 . All subsequent steps are as previously described for test structure  300 . 
     FIG. 5 shows edge emitting laser structure  500  in an embodiment in accordance with the invention. Si-doped GaAs layer  525  with a typical Si doping level in the range of 1.0×10 17 -5×10 18  cm −3 , is grown on GaAs substrate  520 , to a thickness in the range of about 1000-5000 Å at a temperature of about 600-800° C. using TMGa, AsH 3  and Si 2 H 6  under 100 mbar H 2  ambient. Subsequently, Si-doped Al x Ga 1-x As cladding layer  530  where x is in the range of about 0.2 to 0.8, with a Si doping level in the range of 1.0×10 17 -5×10 18  cm −3 , is grown on Si-doped GaAs layer  525  by additionally supplying TMAl to grow Si-doped Al x Ga 1-x As cladding layer  530  to a thickness of about 1.5 μm. The total amount of TMAl supplied is in the range from about 5×10 −4  mol to 2×10 −3  mol. Stopping the TMAl and Si 2 H 6  supply, undoped GaAs non-active layer  535  is grown over Si-doped Al x Ga 1-x As cladding layer  530  to a thickness in the range of about 50-300 Å. Then GaAs 1-x N x  non-active layer  537  where x is in the range of about 0 to 0.1, is grown to a typical thickness of about 600 Å by supplying TMGa, 300 sccm AsH 3  and 500 sccm of NH 3  for typically about 4 minutes while growth temperature is decreased to about 500-600° C. The total amount of NH 3  introduced is typically about 8×10 −2  mol which is more than ten times larger than the amount of TMAl that is typically supplied for the growth of bottom AlGaAs layer  530  in edge emitting laser structure  500  when using MOCVD reactor  120 . GaAs 1-x N x  in non-active layer  537  may be replaced by GaAsP, GaAsNP, InGaP, InGaAsP, InGaAsPN, InGaAsN or similar compounds in accordance with the invention. Also, instead of growth of GaAs 1-x N x  non-active layer  537 , NH 3  flow together with the growth interruption may be used to getter Al. NH 3  flow together with the growth interruption typically results in undoped GaAs layer  538  being grown to a typical thickness in the range of 1000-2000 Å to adjust for missing GaAs 1-x N x  non-active layer  537 . Hence, the thickness of undoped GaAs layer  538  in the NH 3  flow together with the growth interruption case is approximately equal to the combined thickness of GaAs 1-x N x  non-active layer  537  and undoped GaAs layer  538  without growth interruption case. 
     Undoped GaAs layer  538  is grown to a thickness in the range of about 400-1000 Å over GaAsN layer  537  followed by growth of InGaAsN active layer  550  to a thickness in the range of about 60-100 Å at a temperature of about 500-600° C. with TEGa, TMIn, TBAs and DMHy. The ratio of DMHy/(DMHy+TBAs) is typically adjusted to be in the range of about 0.95-0.99 for InGaAsN growth. GaAs barrier layer  555  is grown over InGaAsN active layer  550  to a thickness in the range of about 100-300 Å. Subsequently, InGaAsN active layer  560  is grown over GaAs layer  555  to a thickness in the range of about 60-100 Å. At a temperature of about 500-600° C. with TEGa, TMIn, TBAs and DMHy. The ratio of DMHy/(DMHy+TBAs) is typically adjusted to be in the range of about 0.95-0.99 for InGaAsN growth. After growth of InGaAsN active layer  560 , undoped GaAs wave guide layer  570  is grown to a thickness in the range of about 1000-2000 Å while the temperature is increased to about 600-800° C. C-doped Al x Ga 1-x As cladding layer  580  with x typically in the range 0.2-0.8 and a typical C-doping level typically in the range of 1.0×10 17 -5×10 18  cm −3  is grown on undoped GaAs layer  570  to a thickness in the range of about 1.5-2.5 μm by additionally supplying TMAl and CBr 4  into MOCVD reactor  120 . Finally, heavily C-doped GaAs contact layer  590  with a doping level in the range of 5.0×10 18 -1.0×10 20  is grown over C-doped Al 0.3 Ga 0.7 As layer  580  to a thickness in the range of about 500-2000 Å. 
     Broad-area laser diodes are fabricated from edge emitting laser structure  500  by cleaving facets perpendicular to the direction of light emission. If desired, a dielectric coating may be applied to the cleaved facets. The laser diode size is a laser stripe having a width of about 50 μm with a cavity length of about 500 μm. The threshold current density obtained for the resulting laser diode is typically about 1.23 kA/cm 2  at wavelength of about 1.323 μm. High-quality InGaAsN edge-emitting lasers may be obtained in embodiments in accordance with the invention. 
     FIG. 6 shows vertical cavity surface emitting laser structure  600  in an embodiment in accordance with the invention. Si-doped GaAs buffer layer  625  with a doping level typically in the range of 1.0×10 17 -5.0×10 18  cm 3  is grown on GaAs substrate  620  to a thickness in the range of 1000-5000 Å at a temperature of about 600-800° C. Following growth of Si-doped GaAs buffer layer  625 , bottom n-type DBR mirror structure  630  is grown. N-type DBR mirror structure  630  is typically made up of about 35-45 pairs of alternating layers of which Si-doped Al x Ga 1-x As layer  631  and Si-doped GaAs layer  632  are typical with Si-doping typically in the range of 5.0×10 17 -5.0×10 18  cm −3 . Si-doped Al x Ga 1-x As layer  631  where x is between about 0.8 and 1.0 is grown to a typical thickness corresponding to one quarter of the emission wavelength. Si-doped GaAs layer  632  is grown to a typical thickness corresponding to one quarter of the emission wavelength with about 100-300 Å of grading at each interface. The grading profile is typically linear with distance from the interface. The grading serves to lower hetero barrier between AlGaAs and GaAs layers resulting in lower operating voltages for the VCSEL device. The total amount of TMAl supplied to MOCVD reactor  120  for growth of the AlGaAs layers is typically about 7×10 −3  mol. After completion of the growth for n-type DBR mirror structure  630 , GaAs layer  635  is grown to a typical thickness in the range of about 50-300 Å. Following growth of GaAs layer  635 , growth is interrupted by stopping the supply of TMGa while typically about 300 sccm of AsH 3  is continuously supplied to MOCVD reactor  120  to prevent surface degradation. 
     Then NH 3  is introduced at a flow rate of typically about 500 sccm at a typical temperature and pressure of about 600° C. and 100 mbar, respectively, for approximately 4 minutes. The total amount of NH 3  introduced is typically about 8×10 −2  mol which is approximately ten times larger than the amount of TMAl that is typically supplied for the growth of the Al containing layers that make up DBR mirror structure  630  when using MOCVD reactor  120 . Alternatively, in place of the NH 3  flow, growth of a GaAsN layer may be substituted to getter the Al as discussed previously above. GaAsN may also be replaced, for example, by GaAsP, GaAsNP, InGaP, InGaAsP, InGaAsPN or InGaAsN. After completion of the NH 3  flow, GaAs layer  636  is grown to a thickness of about 1600 Å while the temperature is typically decreased to about 500-600° C. Then InGaAsN quantum well active layer  650  is grown to a thickness in the range of about 60-100 Å using TEGa, TMIn, TBAs and DMHy. The ratio of DMHy/(DMHy+TBAs) in the range of about 0.95-0.99 is typically used for growth of InGaAsN quantum well active layer  650 . GaAs barrier layer  651  is grown over InGaAsN quantum well active layer  650  to a thickness in the range of 50-300 Å. Then quantum well active layer  660  is grown to a thickness in the range of about 60-100 Å using TEGa, TMIn, TBAs and DMHy. The ratio of DMHy/(DMHy+TBAs) in the range of about 0.95 0.99 is typically used for growth of InGaAsN quantum well active layer  660 . GaAs barrier layer  661  is grown over InGaAsN quantum well active layer  660  to a thickness in the range of 50-300 Å. Then InGaAsN quantum well active layer  670  is grown to a thickness in the range of about 60-100 Å using TEGa, TMIn, TBAs and DMHy. The ratio of DMHy/(DMHy+TBAs) in the range of about 0.95-0.99 is typically used for growth of InGaAsN quantum well active layer  670 . The total number of quantum wells as well as the thickness of quantum well active layers  650 ,  660 ,  670  and barrier layers  651 ,  661  may be adjusted to obtain the best results. The distance from the first quantum well active layer, for example, quantum well active layer  650  to the last quantum well active layer, for example, quantum well active layer  670  is fixed to be no greater than 600 Å. The thickness of GaAs cladding layer  636  and GaAs layer  680  is typically adjusted appropriately in order to put the layers extending from the first quantum well layer to the last quantum well layer, for example, quantum well active layer  650  to quantum well active layer  670 , at a maximum of the standing wave cavity. 
     After growth of InGaAsN active layer  670 , GaAs layer  680  is grown to thickness of about 1600 Å while the temperature is typically increased to about 600-800° C. Then p-type DBR mirror structure  690  is grown. P-type DBR mirror structure  690  is made up of about 20-35 pairs of alternating layers of which C-doped Al x Ga 1-x As layer  691  (with x typically between 0.8 and 1) and C-doped Al y Ga 1-y As layer  692  (with y typically between 0 and 0.2) are typical layer pairs and with C-doping typically in the range of 5.0×10 17 -5.0×10 18  cm −3 . C-doped Al x Ga 1-x As layer  691  is grown to a thickness typically corresponding to one quarter of the emission wavelength. C-doped Al y Ga 1-y As layer  692  is grown to a thickness corresponding to one quarter of the emission wavelength with about 100-300 Å of linear grading at each interface. Finally, the growth is completed by growing heavily C-doped GaAs contact layer  695  to a thickness in the range of about 500-1000 Å. C-doped GaAs contact layer  695  is typically doped in the range of 5.0×10 18 -1.0×10 20  cm −3 . 
     Typically, C-doped Al x Ga 1-x As layer  685  is used to make the laterally oxidized layer for the purpose of optical confinement and current confinement. The value of x for C-doped Al x Ga 1-x As layer  685  is selected higher than the value of x selected for any other C-doped Al x Ga 1-x As layer in the structure since the rate of oxidation is strongly dependent on the Al content of C-doped Al x Ga 1-x As layer  685 . See, for example, U.S. Pat. No. 5,896,408, incorporated by reference in its entirety, for details. Ion implantation may also be used to realize current confinement either alone or in conjunction with laterally oxidized layer 
     FIG. 7 shows hetero bipolar transistor structure  700  in an embodiment in accordance with the invention. In this case, no TMAl is introduced prior to the growth of the N containing layers so there is no Al contamination during a single run of the MOCVD reactor. However, in typical commercial applications, reactors are used repeatedly and the MOCVD reactor will typically accumulate residual TMAl from the prior run(s). Hence, a source of Al contamination for the N containing layers will be present after the first run and embodiments in accordance with the invention enhance process reproducibility and reduction of recombination centers in InGaAsN layers  750  and  760  (see FIG.  7 ). 
     Undoped GaAs buffer layer  725  is grown on GaAs substrate  720  to a thickness in the range of 1000-5000 Å. C-doped GaAs subcollector layer  730 , doped in the range of 5.0×10 17 -5.0×10 18  cm −3  is grown on GaAs buffer layer  725  to a thickness in the range of 3000-7000 Å, with a typical thickness of about 5000 Å and at a temperature in the range of 600-800° C. Growth is stopped by turning off the supply of TMGa and CBr 4 . Then, a flow of NH 3  is introduced at a typical flow rate of about 500 sccm along with a flow of AsH 3  at a typical flow rate of about 300 sccm into MOCVD reactor  120 , for a period of approximately 4 minutes while the growth temperature is reduced to the range of about 550-650° C. The selected time and flow rate of the NH 3  assure that the total number of N atoms is greater than the total number of Al atoms introduced into reactor  120  after the last NH 3  flow was introduced in the reactor  120 . After the growth temperature is in the proper range of about 550-650° C. and NH 3  gas flow is stopped, C-doped InGaAsN collector layer  750  is grown to a typical thickness in the range of about 1000-5000 Å on C-doped GaAs subcollector layer  730  with doping levels in the range of 5.0×10 17 -5.0×10 18  cm −3 . Then Si-doped InGaAsN base layer  760  is grown to a thickness in the range of about 500-2000 Å. Si-doping in InGaAsN base layer  760  is typically doped in the range of 5.0×10 17 -5.0×10 18  cm −3 . C-doped AlGaAs emitter layer  780  is typically grown to a thickness in the range of about 500-2000 Å over Si-doped InGaAsN base layer  760 . Undoped AlGaAs spacer layer  770  having a typical thickness of about 50 Å may be inserted between Si-doped InGaAsN base layer  760  and C-doped AlGaAs emitter layer  780  as shown in FIG.  7 . The C-doping level in AlGaAs emitter layer  780  is in the range of 5.0×10 17 -5.0×10 18  cm −3 . Finally, growth is completed by growing C-doped GaAs contact layer  790  to a thickness in the range of about 500-3000 Å. The C-doping level in GaAs contact layer  790  is in the range of about 5.0×10 18 -1.0×10 20  cm −3 . 
     While the invention has been described in conjunction with specific embodiments, it is evident to those skilled in the art that many alternatives, modifications, and variations will be apparent in light of the foregoing description. Accordingly, the invention is intended to embrace all other such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims.