Current isolating epitaxial buffer layers for high voltage photodiode array

Abstract

An array of photodiodes in series on a common semi-insulating substrate has a non-conductive buffer layer between the photodiodes and the semi-insulating substrate. The buffer layer reduces current injection leakage between the photodiodes of the array and allows optical energy to be converted to high voltage electrical energy.

We claim:  
     
         1 . A method for fabricating an array of photodiodes on a semi-insulating substrate; said method comprising: 
 growing a non-conductive, buffer layer on a semi-insulating substrate; and    growing a photodiode structure comprising semiconductor layers on said non-conductive layer.    
     
     
         2 . The method of  claim 1  wherein said semi-insulating substrate and said semiconductor layers comprise a single crystal, direct bandgap semiconductor.  
     
     
         3 . The method of  claim 1  wherein said growing comprises epitaxially growing said buffer layer and/or semiconductor layers on said semi-insulating substrate.  
     
     
         4 . The method of  claim 1  further comprising etching said semiconductor layers to expose said non-conductive, buffer layer or said semi-insulating substrate between said diodes to electrically isolate said photodiodes.  
     
     
         5 . The method of  claim 1  wherein said nonconductor buffer layer is prepared by a low temperature growth method (LTB).  
     
     
         6 . The method of  claim 1  wherein said nonconductor buffer layer is selected from a buffer semiconductor material having a bandgap greater than a bandgap of a semiconductor material of said semi-insulating substrate and greater than a bandgap of said semiconductor layer of said photodiode structure that is in contact with said buffer semiconductor material.  
     
     
         7 . A system for converting optical energy to high voltage electrical energy, said system comprising: 
 a source of optical energy;    means for transmitting said optical energy to an array of independent photovoltaic cells interconnected in series on a surface of a semi-insulating substrate, said cells comprising at least one layer of single crystal semiconductor, and    wherein said independent photovoltaic cells are separated from said semi-insulating substrate by at least one non-conductive buffer layer between a plurality of said photovoltaic cells and said semi-insulating substrate.    
     
     
         8 . The system of  claim 7  wherein said source of optical energy comprises a laser.  
     
     
         9 . The system of  claim 8  wherein said means for transmitting said optical energy comprises a fiber optic.  
     
     
         10 . The system of  claim 9  wherein an optical homogenizer is located between said fiber optic and said array to produce a uniform laser beam profile for illuminence onto said array.  
     
     
         11 . The system of  claim 7  wherein said source of optical energy comprises solar radiation.  
     
     
         12 . The system of  claim 7  wherein said non-conductive buffer layer comprises insulator or semiconductor material not allowing current injection between said substrate and said photodiode during illuminence of said optical energy onto said array.  
     
     
         13 . The system of  claim 7  wherein said non-conductive buffer layer has a resistivity of greater than 1e9 ohm-cm.