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.