Millimeter Wave Reflection Data for Semi-Insulating Gallium Nitride on Sapphire Wafer

In order to estimate the dielectric properties of materials, we need vector measurements consisting of voltage reflection and transmission of electromagnetic radiation for the material under test (amplitude and phase). A recently developed apparatus for measuring time-resolved charge carrier dynamics in photo-responsive materials for millimeter-wave probe frequencies (TR-mmWC) was used to study dc reflection (amplitude only) characteristics of binary III/V direct bandgap material Gallium Nitride (GaN). Commercial-grade 2" N-GaN (Si-doped, high resistivity) on Sapphire wafer with thickness 430 +/- 25 micrometer and GaN layer thickness of 5 micrometers was used to collect reflected RF data using a Schottky barrier diode detector operable in the 110-170 GHz (D-waveguide band) range with responsivity around 2000 volts/watt. Output voltages of this negative polarity detector were collected in steps of 0.01 GHz. Reference voltages (E0) for reflection were collected by using a highly polished mirror. These data can be used to calculate the reflection coefficient (σ) of semi-insulating GaN. Anomalies in reflected voltages were observed in certain frequencies which may be neglected for this type of analysis. These frequencies to be flagged in the dataset are 110.4 GHz, 110.5GHz, 110.7GHz, 114.2 GHz, 114.7GHz, 114.8 GHz, 114.9GHz, 115GHz, 115.2GHz, 115.4GHz, 118.3GHz, 118.7GHz, and 156.4GHz. The cause of these anomalies could be the creation of standing wave/diffraction effects. Data were collected using Keithley digital multimeter operated with LabVIEW, 500 ms sampling period was used and a 30-sample average and standard deviation of signal voltages were stored in an ASCII-delimited comma-separated variable (.csv) file. Data column 1 is probe frequency, column2 is mirror reflected voltage, column 3 is the standard deviation of mirror reflected voltages. Column 4 is the GaN surface reflected voltage obtained at 65.4 degrees and column 5 is the standard deviation of GaN reflected voltage.

为了估算材料的介电特性（dielectric properties），我们需要针对被测材料的电磁辐射电压反射与传输矢量测量结果，该结果需包含幅度与相位信息。本研究采用一款新近研发的、适用于毫米波探针频率下光响应材料时间分辨载流子动力学测量的装置（TR-mmWC），来探究二元III/V族直接带隙材料氮化镓（Gallium Nitride, GaN）的直流反射（仅幅度）特性。实验所用样品为商用级2英寸蓝宝石衬底（Sapphire wafer）上的N型氮化镓（硅掺杂、高电阻率），衬底厚度为430±25微米，氮化镓层厚度为5微米。研究中采用工作于110-170GHz频段（D波导波段，D-waveguide band）、响应度约2000伏/瓦的肖特基势垒二极管检测器（Schottky barrier diode detector）采集反射射频数据。该负极性检测器的输出电压以0.01GHz为步进进行采集。通过使用高抛光镜面采集反射参考电压（E0）。上述数据可用于计算半绝缘氮化镓的反射系数（reflection coefficient，σ）。部分频率下观测到反射电压存在异常，此类异常在本类分析中可予以忽略，对应的异常频率包括：110.4GHz、110.5GHz、110.7GHz、114.2GHz、114.7GHz、114.8GHz、114.9GHz、115GHz、115.2GHz、115.4GHz、118.3GHz、118.7GHz以及156.4GHz，需在数据集中对这些频率进行标记。此类异常的成因可能为驻波/衍射效应（standing wave/diffraction effects）的产生。数据采集使用Keithley数字万用表配合LabVIEW完成，采样周期设为500ms，存储了30次采样的平均值与信号电压的标准差，数据以ASCII分隔的逗号分隔变量（.csv）文件格式保存。数据各列含义如下：第1列为探针频率，第2列为镜面反射电压，第3列为镜面反射电压的标准差，第4列为在65.4度下采集的氮化镓表面反射电压，第5列为氮化镓反射电压的标准差。