Role of surface and interface states on the performance of GaAs based photodetectors

The effect of surface and interface states of various GaAs based structures such as n+GaAs, n-n+GaAs and p-i-n GaAs are investigated for understanding the detector performance. These structures are grown by metal organic vapor phase epitaxy (MOVPE). Surface photovoltage spectroscopy is performed in these structures to investigate the role of surface and interface states on the absorption spectra. Decrease in surface photovoltage signal with increased chopping frequency indicate the presence of slow temporal response states. These states get passivated by growing homo epitaxial layer of GaAs on n+GaAs substrate. Subsequently, for the isolation of surface and interface states on the p-i-n detector structure, n-n+GaAs and p-i-n GaAs structures are investigated separately. Further, the detectors of these structures are developed and their spectral response are recorded at room temperature. The responsivity values are evaluated by varying the incident power of 690 nm laser. Ten times increase in responsivity is observed in p-i-n GaAs photodetector compared to n-n+GaAs photodetector. A low dark current (∼ 0.5 nA) is also obtained in p-i-n GaAs photodetector which qualifies its better device performance.