垂直式與側向式單光子崩潰二極體特性

Abstract

本論文中，我們研究在標準0.18 μm CMOS製程技術下的垂直式與側向式單光子偵測器，從模擬的結果顯示，側向式單光子偵測器採用較低濃度的P-well與N-well可以減少帶間穿隧效應，同時降低元件的暗計數。製作出十五顆元件，分別有著不同的設計參數，如不同的操作偏壓的井及是否含有光柵或是deep n-well﹙DNW﹚結構。量得崩潰電壓約在10 V與15 V 附近，與模擬結果一致。量測並討論元件操作在低於崩潰電壓之下與之上的特性，側向式單光子偵測器有較高的響應及較快的暫態時間，並發現光柵對響應的提升沒有幫助。但元件操作在崩潰電壓之上的特性，側向式單光子偵測器的暗計數比垂直式來的高，與模擬預期的結果不符，我們懷疑較高的暗計數是源自於主動區中出現不想要的淺溝槽隔離﹙Shallow Trench Isolation, STI﹚，由光學顯微鏡﹙Optical Microscope, OM﹚與掃描式電子顯微鏡﹙Scanning Electron Microscope, SEM﹚確認STI的存在。藉由gated-mode的量測，量得在不同超額偏壓的缺陷釋放載子時間﹙de-trapping times﹚，並在足夠長的死亡時間﹙dead times﹚來避開afterpulsing的影響下，量得暗計數及400 nm的光偵側率﹙photon detection efficiency, PDE﹚與等效雜訊功率﹙Noise-equivalent power, NEP﹚。

In this thesis, by using standard 0.18μm CMOS process, we study the vertical and lateral single-photon avalanche diodes (SPADs). Simulation results show that the lower p-typed and n-typed doping concentration in lateral SPADs can reduce the band-to-band tunneling rate so as their dark count rate. Fifteen devices are fabricated with various parameters such as with/without grating, operation voltages, with/without deep n-well (DNW). The measured breakdown voltages of the vertical and the lateral device are about 10 V and 15 V, respectively, which is consistent with the simulated ones. The characteristics of the SPADs biased below and above the breakdown voltages are measured and discussed. The lateral structure has a higher responsivity and fast transient time, comparing with the vertical structure. It is also found that the grating above the device shows no improvement on its responsivity. For the devices performance above breakdown voltages, different from the simulation results, the dark count rate of the lateral structures is much higher than that of the vertical ones. We suspect that much higher dark count rates are caused by the unwanted shallow trench isolation (STI) in the active region, whose existence is observed with optical and secondary electron microscope. By using gated-mode measurement, we have obtained the de-trapping times of the STI-induced traps under various exceed biases. The dark count rates, photon detection efficiency (PDE) and noise equivalent power (NEP) at 400 nm are measured with long enough dead time to avoid afterpulsing effect.