InP/InGaAsP/InGaAs雪崩光電二極體之TCAD模擬、護環效應與暗電流分析

TCAD simulation, guard ring effect and dark current analysis of InP/InGaAsP/InGaAs avalanche photodiode

高英倫(Ying-Lun Kao)

指導教授 ： 林浩雄

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU201904385

摘要

光偵測器的關鍵特性就在於其足夠小的暗電流與光電流增益。對於前者，我們需要了解暗電流成因以設計足夠小暗電流的元件。對於後者，由於SAGCM平面結構之雪崩光電二極體很可能發生邊緣崩潰，降低元件增益。因此，我們需要設計護環（Guard ring）以抑制邊緣崩潰。

為了研究雪崩光電二極體之暗電流成因，本研究首先藉由推演其暗電流成因理論，包括能帶穿隧效應（band-to-band tunneling）與缺陷輔助穿隧效應（trap-assisted tunneling），研究其理論參數之物理意義。並推導出能用以擬合Hurkx缺陷輔助穿隧模型的擬合公式，以了解暗電流成因。接著再藉由半導體工藝模擬軟體（Sentaurus TCAD）建立其物理模型以設計具有最小暗電流之磊晶結構。最後，我們設計了多種護環結構以研究護環效應，包括與中央區接觸的側護環（Attached Guard Ring，AGR），以及不與其接觸的懸護環（Floating Guard Ring，FGR）。

藉由樣品分析，我們發現擴散開口越大者，鋅擴散越淺。較深的側護環元件，有著較大的元件增益與崩潰電壓，也就越能抑制邊緣崩潰。懸護環離側護環越近，增益越小，越無法抑制邊緣崩潰。我們也分析了部分元件之異常電性，提出了會造成提前擊穿、漏電流與崩潰前之降電流等現象之模型。

關鍵字

雪崩光電二極體 ； 護環 ； 暗電流 ； 能井輔助穿隧 ； 能帶穿隧

並列摘要

The key characteristics of photodetector is sufficiently small dark current and large gain. For the former, we need to understand the origin of dark current. For the latter, since it is very likely that the planar SAGCM APD has edge breakdown and thus has smaller gain, we need to design guard ring to supress edge breakdown.

To investigate the origin of dark current, we first derive the dominant dark current mechanisms, including band-to-band tunneling and trap-assisted tunneling. Then we could understand the physics meaning of their modeling parameters. For trap-assisted tunneling, we derive the Hurkx model and the corresponding fitting formula. Second, we use Sentaurus TCAD to simulate the avalanche photodiode, establishing the epitaxial structure which has small enough dark current. Finally, we design various guard ring structures to investigate its effects, including attached guard ring (AGR) and floating guard ring (FGR).

It is found that the larger the diffusion window is, the shallower the diffusion depth is. Deeper attached guard ring has higher gain and breakdown voltage, and thus suppressing edge breakdown. The closer floating guard ring has lower gain. We also analyze the anomalous I-V characteristics and propose the advanced punch through, surface leakage and guard-ring punch through models.

並列關鍵字

Avalanche photodiode ； Guard ring ； Dark current ； Trap-assisted tunneling ； Band-to-band tunneling

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