System and method using migration enhanced epitaxy for flattening active layers and the mechanical stabilization of quantum wells associated with vertical cavity surface emitting lasers

Abstract

Methods and Systems producing flattening layers associated with nitrogen-containing quantum wells and to prevent 3-D growth of nitrogen containing layers using high As fluxes. MEE (Migration Enhanced Epitaxy) is used to flatten layers and enhance smoothness of quantum wells interfaces and to achieve narrowing of the spectrum of light emitted from nitrogen containing quantum wells. MEE is performed by alternately depositing single atomic layers of group III and V before, and/or after, and/or in-between quantum wells. Where GaAs is used, the process can be accomplished by alternately opening and closing Ga and As shutters in an MBE system, while preventing both from being open at the same time. Where nitrogen is used, the system incorporates a mechanical means of preventing nitrogen from entering the MBE processing chamber, such as a gate valve. The gate valve allows the nitrogen source to be completely cut-off from the chamber during non-nitrogen processing steps to achieve the flattening layers described herein. In at least nitrogen containing layers, 3-dimensional growth is also reduced by using high arsenic fluxes, and by using substantially As4 as the main constituent of the arsenic flux.

What is claimed is:  
     
         1 . A method for developing an active region containing nitrogen, said method comprising the steps of: 
 growing at least one nitrogen-free layer by alternately depositing single atomic layers of group III constituents and group V constituents without nitrogen being present, wherein said at least one nitrogen-free layer is substantially flat and suitable for growing layers of semiconductor material containing nitrogen; and    growing at least one nitrogen-containing layer on or near said nitrogen-free layer.    
     
     
         2 . The method of  claim 1  wherein said group III and group V constituents include Ga and As.  
     
     
         3 . The method of  claim 1  wherein said nitrogen-containing layers comprise at least one quantum well.  
     
     
         4 . The method of  claim 3  further comprising the step of providing an arsenic beam equivalent pressure greater than about 1.1e-5 torr during growth of said nitrogen-containing layers.  
     
     
         5 . The method of  claim 3  further comprising the step of providing an arsenic beam equivalent pressure greater than about 1.64e-5 torr during growth of said nitrogen-containing layers.  
     
     
         6 . The method of  claim 3  where an arsenic flux is created during growth of nitrogen-containing layers and comprises predominantly As 4 .  
     
     
         7 . The method of  claim 1  wherein said nitrogen-containing layers comprise a plurality of barrier layers.  
     
     
         8 . The method of  claim 3  wherein said nitrogen-containing layers comprise a plurality of barrier layers.  
     
     
         9 . The method of  claim 7  further comprising the step of providing an arsenic beam equivalent pressure greater than about 1.1e-5 torr during growth of said nitrogen-containing layers.  
     
     
         10 . The method of  claim 8  further comprising the step of providing an arsenic beam equivalent pressure greater than about 1.64e-5 torr during growth of nitrogen-containing layers.  
     
     
         11 . The method of  claim 7  where an arsenic flux is created during growth of nitrogen-containing layers and comprises predominantly As 4 .  
     
     
         12 . The method of  claim 1  wherein said nitrogen-free layers comprise said plurality of barrier layers.  
     
     
         13 . The method of  claim 3  wherein said at least one quantum well includes GaAs, N and at least one of In, Sb and P.  
     
     
         14 . The method of  claim 12  wherein said barrier layer includes GaAs and at least one of In, Sb, and P.  
     
     
         15 . The method of  claim 14  wherein said at least one quantum well includes GaAs and at least one of In, Sb and P.  
     
     
         16 . The method of  claim 15  wherein said at least one quantum well includes N.  
     
     
         17 . A method for processing nitrogen-containing active regions associated with a semiconductor laser, said method comprising the steps of: 
 providing a GaAs substrate;    developing a first confining region including mirror layers above said substrate;    developing an active region including nitrogen containing layers interspersed nitrogen-free layers above said first confining region, wherein said nitrogen containing layers and said nitrogen-free layers are associated with at least one quantum well or at least one barrier layer, said developing an active region further comprising growing at least one nitrogen-free layer by alternately depositing single atomic layers of group III constituents and group V constituents without nitrogen being present, and growing at least one nitrogen containing layer on said at least one nitrogen-free layer; and    developing a second confining region including mirror layers above said active region;    wherein said step of alternately depositing single atomic layers of group III and group V constituents renders a nitrogen-free layer that is substantially flat and useful as a basis for growing at least one nitrogen containing layer.    
     
     
         18 . The method of  claim 17  wherein said group III and group V constituents comprise Ga and As.  
     
     
         19 . The method of  claim 17  wherein said at least one nitrogen containing layer is a quantum well.  
     
     
         20 . The method of  claim 17  wherein said at least one nitrogen containing layer is a barrier layer.  
     
     
         21 . The method of  claim 17  wherein said at least one nitrogen-free layer is a quantum well.  
     
     
         22 . The method of  claim 17  wherein said at least one nitrogen-free layer is a barrier layer.  
     
     
         23 . The method of  claim 19  wherein said quantum well comprises GaAs and at least one of In, Sb and P.  
     
     
         24 . The method of  claim 20  wherein said barrier layer comprises GaAs and at least one of In, Sb and P.  
     
     
         25 . The method of  claim 22  wherein said barrier layer comprises GaAs and at least one of In, Sb and P.  
     
     
         26 . The method of  claim 21  wherein said quantum well comprises GaAs and at least one of In, Sb and P.  
     
     
         27 . The method of  claim 17  wherein said step of alternately depositing single layers of group III and group V constituents is repeated until at least one of a pre-selected time, temperature or number of alternating layers is achieved.  
     
     
         28 . The method of  claim 17  wherein said step of alternately depositing single layers of group III and group V constituents is conducted by alternately opening and closing Ga and As shutters associated with a fabrication system used in said method so that said Ga and As shutters are not both open at the same time.  
     
     
         29 . The method of  claim 17  wherein said step of developing an active region further comprising growing at least one nitrogen-free layer by alternately depositing single atomic layers of group III constituents and group V constituents without nitrogen being present comprises the step of blocking any nitrogen source associated with a fabrication system used for said method.  
     
     
         30 . The method of  claim 29  wherein said blocking any nitrogen source associated with said fabrication system is conducted by deploying a gate valve located along a nitrogen source line leading into said system.  
     
     
         31 . The method of  claim 17  wherein said step of alternately depositing single layers of group III and group V constituents is conducted by alternately opening and closing Ga and As shutters associated with a fabrication system used in said method so that said Ga and As shutters are not both open at the same time.  
     
     
         32 . The method of  claim 17  wherein said step of developing an active region further comprising growing at least one nitrogen-free layer by alternately depositing single atomic layers of group III constituents and group V constituents without nitrogen being present comprises the step of blocking any nitrogen source associated with a fabrication system used for said method.  
     
     
         33 . The method of  claim 32  wherein said blocking any nitrogen source associated with said fabrication system is conducted by deploying a gate valve located along a nitrogen source line leading into said system.  
     
     
         34 . A system for developing an active region containing nitrogen, comprising: 
 a semiconductor wafer processing chamber;    more than one material source lines coupled to said semiconductor wafer processing chamber, wherein said more than one material source lines carry semiconductor processing material into said semiconductor wafer processing chamber, wherein said semiconductor material includes group III and group V constituents;    at least one shutter associated with each of said more than one material source lines and located inside said semiconductor wafer processing chamber;    a nitrogen source line coupled to said semiconductor wafer processing chamber, said nitrogen source line for providing nitrogen into said semiconductor wafer processing chamber; and    a gate valve located on said nitrogen source line, said gate valve for blocking nitrogen from entering said semiconductor wafer processing chamber when deployed to a closed position;    wherein at least one nitrogen-free layer can be grown within said semiconductor wafer processing chamber by operating said at least one shutter associated with each of said more than one material source lines to alternately deposit single atomic layers of said group III and group V constituents while said gate valve is deployed.    
     
     
         35 . The system of  claim 34 , wherein said material source lines provide Ga, As, In, Sb, P and Al.  
     
     
         36 . The system of  claim 34  comprising a molecular beam epitaxy processing system.  
     
     
         37 . The system of  claim 34  comprising a metal-organic chemical vapor disposition processing system.  
     
     
         38 . The system of  claim 34  comprising a metal-organic vapor phase epitaxy processing system.  
     
     
         39 . The method of  claim 1  wherein said nitrogen-free layers comprise said at least one quantum well.  
     
     
         40 . A method for developing an active region for a semiconductor laser containing nitrogen, said method comprising the steps of: 
 growing at least one nitrogen-free layer, wherein said nitrogen-free layer remains substantially along its surface in the absence of nitrogen; and    growing at least one nitrogen containing layer on or near said nitrogen-free layer;    wherein said active region contains layers of nitrogen containing layers interspersed with nitrogen-free layers, said nitrogen containing layers and said nitrogen-free layers being associated with at least one quantum well or at least one barrier layer and wherein said step of growing at least one nitrogen-free layer renders at least one semiconductor layer that is substantially flat and useful as a basis for growing at least one nitrogen containing semiconductor layer.