Photodetectors and optically pumped emitters based on III-nitride multiple-quantum-well structures

Abstract

The design and operation of a p-i-n device, operating in a sequential resonant tunneling condition for use as a photodetector and an optically pumped emitter, is disclosed. The device contains III-nitride multiple-quantum-well (MQW) layers grown between a III-nitride p-n junction. Transparent ohmic contacts are made on both p and n sides. The device operates under a certain electrical bias that makes the energy level of the first excitation state in each well layer correspond with the energy level of the ground state in the adjoining well layer. The device works as a high-efficiency and high-speed photodetector with photo-generated carriers transported through the active MQW region by sequential resonant tunneling. In a sequential resonant tunneling condition, the device also works as an optically pumped infrared emitter that emits infrared photons with energy equal to the energy difference between the first excitation state and the ground state in the MQWs.

1 . A method of operating a sequential resonant tunneling p-i-n device to perform photodetection, said sequential resonant tunneling device comprising a substrate, a p type semiconductor layer, an n type semiconductor layer, an i type semiconductor layer, and a plurality of ohmic contacts comprising metal alloys deposited on surfaces of both the p type semiconductor layer and the n type semiconductor layer, the method comprising: 
 operating the p-i-n device in a sequential resonant tunneling condition to transport electrons through a multiple quantum well region located between the p type and the n type semiconductor layers of the p-i-n device;    applying a bias between the ohmic contacts on the surface of the p type semiconductor layer and the ohmic contacts on the surface of the n type semiconductor layer;    measuring a current-voltage profile of the p-i-n device to determine a working bias;    generating a peak electrical current at the determined working bias during said sequential resonant tunneling; and    performing photodetection at the peak electrical current.    
     
     
         2 . The method of  claim 1 , wherein said p type semiconductor layer comprises one or a plurality of layers selected from the group consisting of: 
 a) a single semiconductor layer of III-nitride materials;    b) a single semiconductor layer of a semiconductor material with a lattice matched to III-nitride materials; and    c) multiple layers of III-nitride materials.    
     
     
         3 . The method of  claim 2 , wherein the number of layers of III-nitride materials is from 2 to 1000.  
     
     
         4 . The method of  claim 1 , wherein said n type semiconductor layer comprises one or a plurality of layers selected from the group consisting of: 
 a) a single semiconductor layer of III-nitride materials; and    b) multiple layers of III-nitride materials.    
     
     
         5 . The method of  claim 4 , wherein the number of layers of III-nitride materials is from 2 to 1000.  
     
     
         6 . The method of  claim 1 , wherein said p type semiconductor layer has: 
 a) a doping level for reaching a hole concentration of at least 1×10 18  cm −3 ; and    b) a thickness of from one hundred nanometers to ten micrometers.    
     
     
         7 . The method of  claim 1 , wherein said n type semiconductor layer has: 
 a) a doping level for reaching an electron concentration of at least 1×10 18  cm −3 ; and    b) a thickness of from one hundred nanometers to ten micrometers.    
     
     
         8 . The method of  claim 1 , wherein said i type semiconductor layer is an active region of the device.  
     
     
         9 . The method of  claim 1 , wherein said i type semiconductor layer comprises multiple quantum well layers of periodically grown units, and wherein each unit comprises one barrier layer and one adjacent well layer.  
     
     
         10 . The method of  claim 9 , wherein said barrier layer and well layer are thin films of III-nitride materials.  
     
     
         11 . The device of  claim 9 , wherein said barrier layer has a larger electronic band gap than said well layer.  
     
     
         12 . The method of  claim 9 , wherein there are a number of units comprising alternating layers of barriers and wells.  
     
     
         13 . The method of  claim 9 , wherein all barrier layers are made of the same III-nitride material and have the same thickness.  
     
     
         14 . The method of  claim 9 , wherein all well layers are made of the same III-nitride material.  
     
     
         15 . The method of  claim 9 , wherein the thicknesses of both said well layers and said barrier layers are from 1 nanometer to 100 nanometers.  
     
     
         16 . The method of  claim 9 , wherein the III-nitride materials comprise group III elements of a predetermined mole fraction of group III element, such that the mole fractions of the group III elements and the thicknesses of said well layers and said barrier layers are specified so that conduction band offset between said well layers and said barrier layers is sufficiently large to produce at least two electron engine states in said well layers, wherein energy positions of said at least two electron engine states are theoretically determined by the effective mass equation,  
       
         
           
             
               
                 
                   
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       where h- is the reduced Planck constant, m* is the electron effective mass, V(z) is the electron potential along the material growth direction, F(z) is the effective-mass envelope function of electrons, and E n  is the energy of electrons at the n th  energy level in the quantum wells.  
     
     
         17 . The method of  claim 9 , wherein said well layers and said barrier layers are semi-insulating.  
     
     
         18 . The method of  claim 9 , wherein the number of units is from 3 to 1000.  
     
     
         19 . The method of  claim 1 , wherein said applying step comprises applying the bias between the ohmic contacts on the surface of the p type semiconductor layer and the ohmic contacts on the surface of the n type semiconductor layer such that said bias produces an electron potential drop from the p type semiconductor layer to the n type semiconductor layer.  
     
     
         20 . The method of  claim 1 , wherein said applying step comprises applying the bias between the ohmic contacts on the surface of the p type semiconductor layer and the ohmic contacts on the surface of the n type semiconductor layer such that said bias produces a near constant electric field in the multiple quantum well region and raises an energy state of a ground state in each well layer to the same level as the energy state of a first excitation state in the adjoining well layer.  
     
     
         21 . The method of  claim 1 , wherein said applying step comprises applying the working bias between the ohmic contacts on the surface of the p type semiconductor layer and the ohmic contacts on the surface of the n type semiconductor layer such that said bias produces photo-generated carriers that are transported by the sequential resonant tunneling through the multiple quantum well region.  
     
     
         22 . The method of  claim 1 , wherein said applying step comprises applying the bias between the ohmic contacts on the surface of the p type semiconductor layer and the ohmic contacts on the surface of the n type semiconductor layer so as to experimentally determined said bias by measuring a current-voltage profile of the device while the peak electrical current exists at the bias.  
     
     
         23 . The method of  claim 1 , wherein said applying step comprises applying the bias between the ohmic contacts on the surface of the p type semiconductor layer and the ohmic contacts on the surface of the n type semiconductor layer such that said bias is adjustable under high power illumination and at different temperatures.  
     
     
         24 . The method of  claim 1 , further comprising the step of alternatively striking said device with absorbing illumination from a back side of said device and a front side of said device.  
     
     
         25 . The method of  claim 1 , further comprising the step of: 
 operating said device as an optically pumped infrared emitter in a sequential resonant tunneling condition,    wherein at least one of the following conditions applies with respect to said infrared emitter:    a) said infrared emitter emits infrared photons created by relaxation of photogenerated electrons from a first excited state to a ground state in the quantum wells, where the energy positions from the first excited states to the ground states are theoretically determined by the effective mass equation                  [       -       ℏ   2       2   m   *         ⁢           ⁢       ∇   2     ⁢     +     V   ⁡     (   z   )             ]     ⁢     F   ⁡     (   z   )         =       E   n     ⁢           ⁢     F   ⁡     (   z   )           ,           where h- is the reduced Planck constant, m* is the electron effective mass, V(z) is the electron potential along the material growth direction, F(z) is the effective-mass envelope function of electrons, and E n  is the energy of electrons at the n th  energy level in the quantum wells;    b) infrared photons emitted by said infrared emitter have an energy in the range of 20 meV to 1.3 eV, with said energy being equal to an energy difference between the first excited state and the ground state in the multiple quantum wells within the device; and    c) said infrared emitter emits an output of M infrared photons for each incident photon going through N quantum wells, where M≦N.