GaN基紫外探测器的光电特性研究

发布时间：2018-04-01 22:28

本文选题：氮化镓　切入点：紫外探测器　出处：《江南大学》2017年硕士论文

【摘要】：作为第三代宽禁带半导体材料的代表,氮化镓(GaN)具有直接带隙、光吸收系数大、抗辐射及耐高温等优良的材料特性,非常适合制备高性能的紫外探测器。这些探测器在导弹飞机预警、燃烧过程检测、工业火焰探测以及环境紫外线检测等领域都有重要的应用价值。由于价格竞争优势,大多数GaN基紫外探测器制备在蓝宝石衬底上,然而标准蓝宝石衬底与GaN外延材料之间存在较大的晶格热失配,薄膜内部往往有较大的位错密度,容易导致较大的反向漏电流密度,增加器件的背景噪音并降低光电转化效率。目前,两种有效改善GaN晶体质量的方法是在图形化蓝宝石衬底(patterned sapphire substrate,PSS)上生长外延层,或者在生长外延层之前先生长缓冲层减小应力。鉴于此,本论文主要在具有PSS和缓冲层衬底的外延片上制备了GaN基紫外探测器,具体的研究内容归纳如下。1、搭建了相关的电学和光学特性测试系统。设计和搭建了高灵敏度的光电流瞬态响应测试系统,该系统具有极小的自响应时间,约为8μs;设计和搭建了低频噪声测试系统,能够实现对低频1/f噪声的精确测量;此外,从增强光源功率和减小光传输衰减两个方面入手,优化了光谱响应测试系统。2、在基于PSS且掺杂渐变的GaN外延片上制备了肖特基型紫外探测器。与传统结构的器件相比,该器件表现出了显著改善的电学和光学特性:室温下,当偏压为-5 V时,器件具有极低的暗电流密度~1.3×10~(-8) A/cm~2,在正向低偏压下,随着温度的升高,电流输运机制由隧穿为主变为扩散与复合电流共同作用;在零偏压下,紫外/可见光抑制比为~4.2×10~3,最高的响应度为~0.147 A/W,最大外量子效率为~50.7%,甚至在深紫外波段(360 nm-250 nm)平均量子效率也大于40%;开启时间和关闭时间约为~115μs和~120μs,基本不随偏压变化,且具有很好的热稳定性;零偏压下热噪声限制的极限探测率为~5.5×10~(13) cm·Hz~(1/2)/W,-5 V偏压时探测率约为~6.72×10~(10) cm×Hz~(1/2),同已报道的相似结构器件的最高探测率处于同一个水平。3、制备了AlGaN基金属-半导体-金属型紫外探测器。通过在传统蓝宝石衬底和AlGaN外延层之间高温生长AlN作为缓冲层来提高晶体质量。结果表明:器件具有极低的暗电流~8 pA;在10 V电压下的响应度约为~0.07A/W,量子效率为~41.5%;器件的平均开启时间和关闭时间约为~111μs和~77μs;热噪声限制的极限探测率为~4.89×10~(12) cm·Hz~(1/2)/W,-5 V偏压时,器件探测率约为~6.26×10~9 cm×Hz~(1/2)。同时,还对器件进行了电压应力退化实验,发现暗电流及响应度随应力时间逐渐减小,但静置一段时间后,光电参数又可恢复至受应力前水平,推测可能是材料内部的陷阱效应所导致。
[Abstract]:As the representative of the third generation wide band gap semiconductor materials, gallium nitride (gan) has many excellent properties, such as direct band gap, large optical absorption coefficient, radiation resistance and high temperature resistance. Very suitable for the preparation of high performance UV detectors. These detectors have important applications in missile aircraft early warning, combustion process detection, industrial flame detection and environmental ultraviolet detection. Most GaN based UV detectors are fabricated on sapphire substrates. However, there is a large lattice thermal mismatch between standard sapphire substrates and GaN epitaxial materials. At present, two effective methods to improve the quality of GaN crystals are to grow epitaxial layers on patterned sapphire substrates on graphical sapphire substrates. Or the buffer layer is grown to reduce the stress before the epitaxial layer is grown. In view of this, the GaN based UV detector is prepared on the epitaxial wafer with PSS and buffer substrate. The specific research contents are summarized as follows: 1. A related electrical and optical characteristic testing system is built. A high sensitivity photocurrent transient response test system is designed and built. The system has minimal self-response time. It is about 8 渭 s. The low frequency noise measurement system is designed and built, which can accurately measure the low frequency 1 / f noise. In addition, it starts from two aspects: enhancing the power of light source and reducing the attenuation of optical transmission. Schottky type UV detector was fabricated on the GaN epitaxial wafer based on PSS and doped with gradient. Compared with the traditional device, the device showed significantly improved electrical and optical properties: at room temperature, the optical and electrical properties of the device were improved. When the bias voltage is -5 V, the device has a very low dark current density of 1.3 脳 10 ~ (-8) A / cm ~ (-2). At the positive low bias voltage, the current transport mechanism changes from tunneling to diffusion and composite current with increasing temperature, and at zero bias voltage, The UV / VIS ratio is 4.2 脳 10 ~ (-3), the highest responsivity is 0.147 A / W, and the maximum external quantum efficiency is 50.7, even in the deep ultraviolet band, the average quantum efficiency is more than 400.The opening time and closing time are about 115 渭 s and 120 渭 s, which basically do not change with bias voltage. And has good thermal stability; The limit detectivity of thermal noise limit under zero bias voltage is 5.5 脳 10 ~ (10) ~ (13) cm ~ (-1 / 2) / W ~ (-5) V bias. The detection rate is about 6.72 脳 10 ~ (10) ~ (10) cm 脳 10 ~ (10) cm ~ (-1) ~ (2) ~ (-1) ~ (-1) ~ 2 ~ (-1), which is at the same level as the reported maximum detectivity of similar structure devices. The AlGaN based metal-semiconductor-metal violet has been prepared. External detectors. The crystal quality is improved by growing AlN as a buffer layer between the traditional sapphire substrate and the AlGaN epitaxial layer. The results show that the device has a very low dark current of 8 Pa, and the responsivity is about 0.07 A / W at 10 V voltage. The quantum efficiency is 41.5; the average opening time and closing time are about 111 渭 s and 77 渭 s; the limit detectivity of thermal noise limit is 4.89 脳 10 ~ (-1) cm ~ (-1 / 2) / W ~ (-5) V bias voltage. The detection rate of the device is about 6.26 脳 10 ~ 9 cm 脳 Hz ~ (-1 / 2). At the same time, the voltage stress degradation experiments are carried out. It is found that the dark current and the responsivity decrease gradually with the stress time, but after a period of time, the optoelectronic parameters can be restored to the pre-stress level. It is speculated that the trap effect inside the material may be the result.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN23

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