單光子雪崩偵測器(single-photon avalanche diode, SPAD)具有體積小、成本低、速度快以及操作容 易的優點，且元件本身具有相當大的增益，以致能達到單光子感測的靈敏度，相當適合被開發應用於量子 資訊科學、量子金鑰分配等領域；近年來，矽製程製作的SPAD 逐漸成熟且已應用於光雷達測距以及生醫檢 測，但Si SPAD 僅能偵測1.1μm 以下的光。三五族SPAD 可操作於近紅外光波段，在偵測時能避免受到環 境背景光影響，於應用上更顯其競爭力。本計劃致力於新型InGaAs/InAlAs SPAD 的開發，以InAlAs 取代 InP 作為放大區具備許多優點：(1)崩潰電壓有較好的溫度穩定性、(2)雪崩崩潰機率較高、(3)mesa 結構易 於延伸至陣列等。計劃將從磊晶著手，改善磊晶品質以降低缺陷密度，並系統性透過模擬與磊晶回饋最佳 化結構與設計製程，以期開發出一低暗計數、高光偵測率、反應時間快的元件；立基於特性良好之元件開 發，我們會以弦波閘極偏壓搭配簡諧減除與自我差分法縮短元件的關閉時間，達到高頻操作；並進一步結 合閘極偏壓操作與被動崩潰截止及主動重置電路，減少雪崩產生之載子數目，進而抑制二次崩潰機率以實 現低暗計數且高速操作之SPAD 元件；最後，將單一元件延伸至多像素陣列，配合多通道單光子計數與時間 關聯統計技術，達成遠距離光雷達測距及光學相干斷層掃描之應用。 ;Single-photon avalanche diodes (SPADs) have several advantages including small size, low cost, high speed and easy operation. SPADs also provide considerably large current gain, so that they can detect the weak light down to single-photon level, revealing capacity in the applications of quantum information science and quantum key distribution. In the recent years, SPADs fabricated in standard CMOS technology have become mature and have been demonstrated in the applications of laser detection and ranging (LADAR) as well as the medical diagnostics. However, silicon based SPAD only allows the detection of light below 1.1 μm. III-V based SPAD capable of detecting near infrared light can perform well even under the strong ambient light. They are promising in the applications of eye-safe laser ranging. This project devotes to the development of InGaAs/InAlAs based SPADs which use a multiplication layer of InAlAs instead of InP because InAlAs offers better temperature stability of avalanche breakdown, higher avalanche breakdown probability and easier fabrication of multi-pixel array due to mesa-structure. This project commences with the improvement of material quality for reducing the defect density and then makes effort on the structure design, optimization, and fabrication technology in a systematical way based on TCAD simulations, aiming to develop a superior SPAD device with low dark count rate and high photon detection efficiency. After the development of devices with high performance, we use the scheme of sine wave gating combining with the method of harmonics subtraction and self-differencing to achieve high-frequency operation. We will further improve the afterpulsing effect by integrating the method of passive quenching and active reset into the gated-mode operation. Ultimately, we plan to extend a single device to a multi-pixel array and perform the applications of long-distance LADAR and optical coherence tomography (OCT) with the aid of technology of multi-channel single photon counting and time correlated histogram.
