[论文解读] Optimization of Amorphous Germanium Electrical Contacts and Surface Coatings on High Purity Germanium Radiation Detectors

M. Amman|arXiv (Cornell University)|Jan 1, 2018

Advanced Semiconductor Detectors and Materials参考文献 46被引用 16

一句话总结

本文针对高纯度锗（HPGe）辐射探测器中的电极接触层和表面钝化层，优化了非晶态锗（a-Ge）薄膜的性能。通过调节射频溅射过程中的溅射气压和氢气含量，研究确定了可最小化漏电流、稳定电子势垒高度并提升室温稳定性的工艺参数——这些特性对用于成像与追踪应用的高性能伽马射线探测器至关重要。

ABSTRACT

Semiconductor detector fabrication technologies developed decades ago are widely employed today to produce gamma-ray detectors from large volume, single crystals of high purity Ge (HPGe). Most all of these detectors are used exclusively for spectroscopy measurements and are of simple designs with only two impurity based electrical contacts produced with B implantation and Li diffusion. Though these technologies work well for the simple spectroscopy detectors, the Li contact in particular is thick and lacks room temperature stability in a manner that makes it inappropriate for many of the more complex detectors needed for gamma-ray imaging and particle tracking applications. Thin films of amorphous semiconductors such as sputter deposited amorphous Ge (a-Ge) are the basis for an alternative electrical contact that is easy to fabricate, thin, and can be finely segmented. The a-Ge also functions well as a passivation coating on the HPGe surfaces not covered by the electrical contacts. The properties of the a-Ge affect the performance of the resultant detectors, and these properties substantially depend on and are controllable through the sputter deposition process parameters. The subject of this paper is this interconnection of fabrication process parameters, a-Ge properties, and detector performance. The properties of a-Ge thin film electrical resistance, a-Ge contact electron injection, and room temperature storage stability were evaluated as a function of the sputter process parameters of sputter gas pressure and sputter gas H2 composition. Two different sputter deposition systems were used to produce a-Ge resistors and HPGe detectors with a-Ge electrical contacts. These samples were electrically characterized as a function of temperature. A summary of this study and discussion of the relevance of the findings to the optimization of detector performance are given in this paper.

研究动机与目标

• 提升高纯度锗（HPGe）辐射探测器的性能与稳定性，以满足伽马射线成像与粒子追踪等先进应用的需求。
• 解决传统锂漂移接触层因厚度大且在室温下不稳定而带来的局限性。
• 优化非晶态锗（a-Ge）薄膜，作为分段式电极接触与表面钝化层的可行替代方案。
• 识别控制a-Ge薄膜关键性能参数（如电阻率、电子注入与漏电流稳定性）的溅射沉积工艺参数。
• 建立a-Ge薄膜的工艺-结构-性能关系，以实现可重复、高良率的探测器制造。

提出的方法

• 采用射频溅射在HPGe衬底上沉积a-Ge薄膜，并对溅射气体压力和氢气含量进行受控调节。
• 使用两套独立的溅射沉积系统，以验证不同设备下工艺参数影响的一致性。
• 在多种温度下进行电学表征，以评估电阻率、电荷注入与漏电流行为。
• 基于金属-半导体接触理论（ACS理论）建立理论模型，用于解释电子势垒高度与注入特性。
• 将薄膜的微观结构与电阻率关联，以识别电学性能的结构根源。
• 评估后处理退火处理对长期稳定性与性能的影响。

实验结果

研究问题

• RQ1 溅射气体压力与氢气含量如何影响a-Ge薄膜在HPGe探测器上的电阻率与电学稳定性？
• RQ2 a-Ge薄膜的微观结构（如柱状结构、富孔结构）与其电学性能（如电阻率与漏电流）之间存在何种关系？
• RQ3 室温储存对a-Ge接触层的电子势垒高度与电荷注入有何影响？这些影响能否通过工艺调节最小化？
• RQ4 在制造过程中进行的高温退火步骤在多大程度上改变了a-Ge薄膜的电学与钝化性能？
• RQ5 能否同时使用可变范围跳跃模型（用于电阻层）与ACS理论（用于接触层）对a-Ge薄膜中的电荷输运机制进行一致建模？模型参数是否一致？

主要发现

• 高溅射气体压力导致a-Ge薄膜具有更高的电阻率，可能源于更开放的柱状微观结构与更高的孔隙密度。
• 在溅射气体中引入氢气可降低电子势垒高度并增加漏电流，其稳定性取决于压力与H2浓度。
• a-Ge薄膜在室温储存过程中表现出可测量的电子注入与势垒高度变化，表明存在工艺相关的老化效应。
• a-Ge薄膜的电阻率强烈依赖于溅射压力，高压条件下电阻率显著升高。
• 基于ACS理论的理论建模成功描述了电子注入行为，且与可变范围跳跃模型的一致性得到验证，支持对电荷输运的统一理解。
• 在100–120°C下进行的后处理退火未能逆转性能退化，但结果表明可通过优化工艺配方实现加工后性能的稳定。