Dual-band InGaAs nBn photodetectors at 2 mu m

An nBn type InGaAs photodetector structure operating at 2 mu m with dual-band operation capability has been numerically designed and experimentally characterized. A compositionally graded and unintentionally doped InGaAlAs layer with a delta-doped nano-layer behaves as the barrier for majority carrier flow. The pixels fabricated with a 20 mu m pitch mesa process yielded peak quantum efficiencies of 67% and 53% without anti-reflective coating for the e-SWIR and SWIR sides, respectively. Dark current measurements on a large area pixel yield 3.40 mA/cm(2) at 300 K and 0.61 mu A/cm(2) at 200 K for the e-SWIR side, while 8.05 mu A/cm(2) at 300 K and 1.09 nA/cm(2) at 200 K are obtained for the SWIR side. I-V characteristics analysis performed with pixels having different areas shows that the designed nBn structure has no surface leakage current presenting a potential benefit for dual-band applications requiring mesa structures that usually suffer from surface states for the InGaAs material system. Temperature dependent dark current characterization confirms this result and implies diffusion current dominated dark current.