Aluminum gallium nitride/silicon carbide separate absorption and multiplication avalanche photodiodes

Deep ultraviolet (DUV) avalanche photodiodes (APD) sensitive at wavelengths shorter than 260 nm have numerous applications, including chemical and biological identification and water quality monitoring. Wide bandgap materials such as silicon carbide (SiC) and the III-nitrides (AlInGaN) are well suited for UV detector applications. SiC devices have high avalanche gain, low dark current and low excess noise owing to a low k-factor (k=0.01) due to the much higher impact ionization coefficient for holes relative to electrons; however, these devices have poor response at wavelengths shorter than 260 nm related to carrier trapping by surface states. Conversely, the III-nitrides have a direct bandgap which can be engineered for efficient absorption in the DUV regime, but suffer from high leakage currents, especially for lattice mismatched growth, and difficulty in p-type doping in high AlN mole fraction alloys. To overcome these challenges, this work targets separate absorption and multiplication avalanche photodiodes (SAM-APDs) utilizing an aluminum gallium nitride (AlxGa1-xN) absorption layer and a SiC multiplication region.