氮化鎵金屬-半導體-金屬光偵測器的製作與特性分析

Abstract

柵狀結構(interdigitated)紫外光導式光偵測器、金屬-半導體-金屬(MSM)光偵測器和透明電極MSM光偵測器已經成功的製作於n型氮化鎵基板。元件操作特性的量測包含光偵測器對於照射光源波長的響應 (光譜響應)，光源調製頻率的響應(交流響應)和外加偏壓的響應 (直流響應)等已經完成並且加以分析。所有光偵測器的光譜響應在波長約364nm(即氮化鎵能隙邊緣)截止之前，都展現出短波長範圍的偵測能力。光導式光偵測器和MSM光偵器的交流響應訊號都隨光源調制頻率增加而減小，由光導式光偵測器交流響應實驗結果擬合出氮化鎵基板的過量載子生命期約為5msec。在進行光導式光偵測器光譜響應實驗的同時，另加以氦氖雷射(6328nm)照射光偵測器，發現響應光電流有降低的現象。受體似（acceptor-like）深層能階的電洞捕捉可能是造成長時間的過量載子生命期和光譜響應實驗的光電流降低現象的原因。對於波長325nm的入射光源，光導式光偵測器在0.5V直流偏壓下最大的響應度約為82.4A/W ，MSM 和透明電極MSM光偵測器在8V的直流偏壓下最大的響應度分別約為2.47A/W 和3.29A/W，推測由於光導增益使得直流響應的光電流有顯著的放大效果。

Interdigitated ultraviolet photoconductive detectors, conventional metal-semiconductor-metal (MSM) photodetectors, and transparent-electrode MSM photodetectors were successfully fabricated on n-GaN wafers. Photo response on wavelength (spectral responsivity), chopper frequency (ac response) and bias voltage (dc response) had been extensively investigated. Responsivity spectra of all type detectors had sharp edge at wavelength around 364 nm, and dropped with a tail in wavelength greater than 364 nm, which is equivalent to the energy gap of GaN. Ac response of photoconductive detectors and MSM photodetectors decayed with the increasing chopping frequency, indicating a large excess carrier lifetime. Optical quenching effect was observed on the responsivity spectra for the photoconductive detectors illuminated simultaneously with He-Ne laser (6328nm). Acceptor-like deep levels trapping the holes was attributed to the main effect to large carrier lifetime and optical quenching phenomenon. Photoconductive detectors, conventional MSM photodetectors, and transparent-electrode MSM photodetectors have maximum dc responsivity (with detection wavelength of 325 nm) of 82.4A/W at 0.5V, 2.47A/W at 8V, and 3.29A/W at 8V, respectively. For the large excess carrier lifetime, photoconductive gain effect was ascribed to the resulting photocurrent amplification for these three type photodetectors.