| dc.description.abstract | 單光子崩潰二極體(Single-photon avalanche diode, SPAD)應用範圍很廣，從消費性電子、家用電器、車用電子、無人機涵蓋至醫療檢測儀器，都需要高精確度的光偵測器。隨著工業4.0的產業轉型以及無人化產業蓬勃，促使光學雷達的快速發展，其亟需一極為靈敏又反應快速的感測裝置，本論文所研究之雪崩單光子崩潰二極體遂相當具有潛力，可望帶來極高市場價值。
以矽材料為基礎的CMOS SPAD的開發最早也相當成熟，但由於受限於矽的能隙大小，僅能偵測可見光至近紅外光波段；為了光纖通訊的相關應用，需採用1310 nm以及1550 nm的雷射光做為光源，此波段的光對人眼視網膜的傷害相較於可見光低很多，因此本論文著力於III-V SPAD的開發；於此論文中，我們以砷化銦鎵(InGaAs)做為吸收層，但因InGaAs能隙太小，易產生穿隧效應導致漏電流，故以能隙較大的材料做為放大層，並採取吸收層與放大層分離的結構(Separation absorption, grading, charge, multiplication, SAGCM)；早期多數研究皆使用磷化銦(InP)做為放大層，近年來的文獻透過計算得知砷化銦鋁(InAlAs)具有較高崩潰機率以及崩潰電壓對溫度穩定性好，因此本論文採用InAlAs做為放大層，期望能提高光偵測效率以及電壓對溫度之穩定性。
本論文比較了兩種不同元件製程結構：Double-mesa和Triple-mesa，在抑制邊緣電場上的效果，由暗電流量測結果可得知，Triple-mesa比起Double-mesa的SPAD元件有較低的暗電流，另由SPAD元件的暗計數可得知此兩種結構Triple-mesa的暗計數率也相對較低；此外，元件響應度(Responsivity)與光偵測效率(photon detection efficiency)過低，判斷係因磊晶厚度控制以及摻雜擴散的問題，吸收層沒有確實達到擊穿電場值以及放大層厚度因電荷層摻雜擴散被壓縮，故本論文亦利用Silvaco TCAD軟體以進一步調整各層最佳參數，改變了電荷層的厚度與摻雜濃度以及放大層的厚度，並維持吸收層厚度，以確認摻雜濃度擴散對元件所造成的影響；我們也透過各種參數設計，確立了電荷層厚度減少可以增加摻雜濃度浮動的可容忍範圍；換言之，一旦電荷層厚度增加，對摻雜濃度的要求就更為嚴格，這解釋了磊晶時的摻雜擴散是元件喪失單光子偵測特性的主因。 | zh_TW |
| dc.description.abstract | Single-photon avalanche diodes (SPAD) are widely used in several territories from consumer electronics, household appliances, automotive electronics, drones to medical diagnostic equipment, which all require a high sensitivity detector. The growing demand of industrial transformation of Industry 4.0 and unmanned industry facilitate the development of optical radar, also called LiDAR (light detection and ranging). An extremely sensitive and fast-response sensor is urgently needed. The SPAD studied in this study has great potential and is expected to produce high market value.
The development of CMOS SPAD based on silicon materials is quite mature, but limited by the bandgap of silicon, it can only detect the light covering from visible to near-infrared wavelength range. For the applications of optical fiber communication, 1310nm and 1550nm lasers are often used as light sources. The short-wave infrared light is less harmful to the human eye than visible light, permitting the eye-safety applications. Therefore, we focus on the development of III-V SPAD. In this study, InGaAs is used as the absorption layer, but the energy bandgap of InGaAs is small, which may cause serious tunneling effect and result high leakage current. A material with larger bandgap the should be chosen as the multiplication layer, so a typical structure of separating the absorption layer and the multiplication layer is adopted for the III-V avalanche photodiodes (APDs) or SPADs. Most of the early research used InP as the multiplication layer. In recent years, the calculations from the literature shows that InAlAs has a higher probability of breakdown and has less dependence of breakdown voltage on the temperature. Therefore, this study uses InAlAs as the multiplication layer, which is envisioned to improve the photo detection efficiency and the temperature stability of breakdown voltage.
This thesis studies the effect of mesa structures on the suppression of peripheral electric field of SPAD, and the characteristics of SPAD with double-mesa and triple-mesa structure are compared. From the dark current measurement results, it can be obtained that SPAD with triple-mesa structure has a lower dark current than SPAD with double-mesa structure. In addition, the dark count rate of SPAD with triple-mesa structure can be better suppressed. However, the responsivity and photon detection efficiency are accidentally poor, which is preliminary attributed to the issue of layer thickness control and doping diffusion during epitaxy. The epitaxy issue may cause a reduced multiplication layer thickness and incomplete depletion of the absorption layer. To further examine the possible causes of low photon detection efficiency, we calculate the electric field in the SPAD structures under several parameter settings by using Silvaco TCAD tools. By changing the thickness and doping concentration of the charge layer and the thickness of the multiplication layer, where the thickness of the absorption layer remains the same, the proper operation window between breakdown and punch-through voltage is obtained. According to the result, we can conclude that a thicker charge layer has less tolerance on the doping concentration. As a result, the thickness variation and the diffusion of the doping concentration has fatal influence on the SPAD performance. | en_US |