Optical Performance of Two Dimensional Electron Gas and GaN:C Buffer Layers in AlGaN/AlN/GaN Heterostructures on SiC Substrate

Roman B Adamov,Paweł Prystawko,Maxim Ya Vinnichenko,Vytautas Janonis,Saulius Tumėnas,Justinas Jorudas,Marcin Krysko,Irmantas Kašalynas,Vadim A Shalygin,Daniil Pashnev,Maciej Sakowicz,Maria D Moldavskaya

doi:10.3390/app11136053

Abstract

Terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy were developed as the method for the investigation of high-frequency characteristics of two-dimensional electron gas and GaN:C buffer layers in AlGaN/AlN/GaN heterostructures grown on a semi-insulating SiC substrate. The reflectance and transmittance spectra of the selected heterostructure layers were studied after the top layers were removed by a reactive ion etching. Results were numerically analyzed using the transfer matrix method taking into account the high-frequency electron conductivity via a Drude model and complex dielectric permittivity of each epitaxial layer via a one-phonon-resonance approximation. Good agreement between the experiment and theory was achieved revealing the temperature dependent electron effective mass in AlGaN/AlN/GaN high electron mobility transistor structures and the small damping factors of optical phonons due to high crystal quality of the epitaxial layers fabricated on the SiC substrate.

Highlights

The transverse optical (TO) phonon damping factors were used as variable parameters fitting simulated data to the experimental reflectance spectra
The spectrum was modelled assuming that the amplitude of the reflectance peak in the vicinity of TO phonon resonance of AlN layer is controlled by the damping factor γ4 while the interference pattern in the wavenumber range of 450–555 cm−1 is defined by the d30 and γ3 parameter values of the GaN:C layer possessing the TO phonon resonance at 559 cm−1
The infrared-terahertz spectroscopy method has been developed for the investigation of optical performance of 2DEG and GaN:C buffer layers in the AlGaN/AlN/GaN

Summary

Introduction

Interest in two-dimensional (2D) materials, plasmonic and polaritonic devices increases continuously [1,2,3]. It stimulates the progress of non-destructive test methods used in the infrared (IR) band and terahertz (THz) frequency range [4,5]. Remote monitoring of high-frequency characteristics of selected heterostructure layers would allow for smarter development of novel materials and devices with optimized performance in the IR band and THz frequency range [9,12,13,14]

Methods

Results

Conclusion