Probing Electron Density in Quantum Wells and its Impact on the Performance of Infrared Photodetectors

For quantum well (QW) photodetectors and lasers, doping to obtain desired electron density in QWs is a critical factor to realize the optimal device behavior. In this study, we employed scanning spreading resistance microscopy (SSRM) to resolve the carriers in individual QWs, and investigate the relevance between carrier concentration and the performance of three Quantum Well Infrared Photodetectors (QWIPs) with n-type density designed as ${2}.{5} \times {10} ^{{17}}$ cm $^{-{3}}$ , ${5} \times {10} ^{{17}}$ cm $^{-{3}}$ and ${2} \times {10} ^{{18}}$ cm $^{-{3}}$ respectively. It’s found that the actual dopant densities of silicon in QWs obtained by secondary ions mass spectroscopy (SIMS) can be considerably deviate from the nominal values. Meanwhile the electron concentrations in QWs estimated from the SSRM measurement are ${2}.{4} \times {10} ^{{17}}$ cm $^{-{3}}$ , ${4}.{7} \times {10} ^{{17}}$ cm $^{-{3}}$ and ${1}.{0} \times {10} ^{{18}}$ cm $^{-{3}}$ respectively, which accounts for the increment of the responsivity and the degradation in dark current among the three QWIPs. The SSRM study dicloses the insuffcient activation of Si dopant in nano-sized GaAs QWs, and in another aspect, it confirms the optimal carrier concentration for realizing ideal signal-to-noise ratio of the QWIPs.