Minority carrier diffusion in InGaAs/InP P–i–N heterojunctions for photodetector arrays

InGaAs/InP double-heterostructure P–i–N diodes of various junction areas are characterized at room temperature and modeled using TCAD. Biasing the guard ring allows one to quantify the dark current contributions to the central diode from Shockley–Read–Hall (SRH) generation in the depletion region as well as the junction perimeter leakage. The latter is determined to be 1.4 ± 0.3 pA/cm based on an interface trap density of 106 cm−2 at the InGaAs/InP interface, whereas the depletion region contributes 2.0 ± 0.2 nA/cm2 based on a nonradiative SRH lifetime of 0.8 ms. Unbiasing the test structures results in up to an order of magnitude increase in dark current due to minority carrier diffusion; modeling yields a minority carrier diffusion length of 70 µm, which is in agreement with the experimentally extracted value of (65 ± 5) µm using separate test structures on the same wafer. This corresponds to a hole mobility of 570 cm2/Vs at room temperature for a doping concentration of 5 × 1015 cm−3. The calibrated model is then verified by predicting the dark current of 25 × 25 and 15 × 15 μm2 pixels; the results are in good agreement compared to measurements of 100 pixel test arrays.