Ultrafast responses of uniform- and gradient-doped GaAs photocathodes: from theory to experiment

Rui Zhou; Hemang Jani; Yijun Zhang; Yunsheng Qian; Lingze Duan

doi:10.1117/12.2607632

7 March 2022 Ultrafast responses of uniform- and gradient-doped GaAs photocathodes: from theory to experiment

Rui Zhou, Hemang Jani, Yijun Zhang, Yunsheng Qian, Lingze Duan

Proceedings Volume 11999, Ultrafast Phenomena and Nanophotonics XXVI; 119990C (2022) https://doi.org/10.1117/12.2607632
Event: SPIE OPTO, 2022, San Francisco, California, United States

Abstract

Semiconductor photocathodes with gradient-doping structures have attracted lots of interest in recent years because of their improved performances, such as higher quantum efficiency and longer diffusion length, over uniform-doped devices. It has been suggested that such improvement is due to the built-in electric field generated by the gradient of the doping concentration in the active layer. Under this built-in field, photoelectrons migrate toward the device surface via both diffusion and directional drift. While some past reports have studied and compared the photoelectron behaviors in uniform- and gradient-doped GaAs photocathodes, most of them are based on steady-state measurement and analysis. There has been little prior work focusing on dynamic responses. In this presentation, we report a comparative study of the ultrafast response of a uniform-doped and a gradient-doped GaAs photocathode, both theoretically and experimentally. We first develop a generalized diffusion-drift model, which adds a built-in electric field to a carrier diffusion model to incorporate the carrier drift. Then the theoretical model is used to predict the ultrafast transient behaviors of photoelectrons in both uniform- and gradient-doped photocathodes. Finally, the transient reflectivity of the photocathode devices is experimentally measured using pump-probe reflectometry (PPR), and the results are compared to the theoretical predictions. These comparisons indicate that the theoretical model is able to offer an appropriate physical picture of carrier transportation inside GaAs photocathodes of different doping profiles. It also enables the evaluation of device parameters such as diffusion coefficient and carrier decay time via PPR measurement.

Conference Presentation

Citation Download Citation

Rui Zhou, Hemang Jani, Yijun Zhang, Yunsheng Qian, and Lingze Duan "Ultrafast responses of uniform- and gradient-doped GaAs photocathodes: from theory to experiment", Proc. SPIE 11999, Ultrafast Phenomena and Nanophotonics XXVI, 119990C (7 March 2022); https://doi.org/10.1117/12.2607632

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