Low-Temperature Geiger-Mode Characterization of a Gallium Nitride p-i-N Avalanche Photodiode

We present the low-temperature Geiger-mode characteristics of GaN (gallium nitride) p-i-n avalanche photodiodes (APDs). The devices have a breakdown voltage of -95V and a temperature dependence of similar to 0.0159 +/- 0.0034 V/K near 300K. The room-temperature (300 K) dark-count rate (DCR) is 23.8 MHz for a 75 x 75 mu m(2) device biased at 1 % overvoltage. The DCR halves when lowering the temperature by 50. C. Based on the temperature-dependent characteristics of the DCR, we identify band-to-band tunneling as the dominant DCR generation mechanism. At 4.65 % overvoltage and 375 nm, the photon detection efficiency (PDE) is 0.82 %- limited by a low breakdown probability of 1.7 %. We discuss the measurement setup and the method to extract count rates, which is based on the Poisson distribution of the time intervals between Geiger-mode breakdowns of the APD. The setup includes a custom circuit to bias the diode and amplify its signals, a steady ultraviolet (UV) light source, and a system to control the temperature of the APD with a thermoelectric element in the range from -40 to 20 degrees C.