Terahertz Electroluminescence of Shallow Impurities in AlGaN/GaN Heterostructures at Temperatures above 80 K

Abstract

In this work terahertz (THz) electroluminescence of shallow impurities in AlGaN/GaN high electron mobility transitor (HEMT) structures are studied at temperatures above 80 K. The samples are excited with electric field pulses of up to 300 V cm−1 and duration of normalτp=1.6 ms. The THz emission spectra are measured in vacuumed environment by means of infrared Fourier transform spectroscopy. Resonant 1s − 2p electron transitions in energy levels of residual oxygen and silicon impurities are observed at temperatures above 80 K. A comparison of the area under the shallow impurities electroluminescence signal correlates with the growth conditions of the AlGaN/GaN heterostructures. In such a way a method to monitor the ratio between ionized shallow impurities in unintentionally doped AlGaN/GaN HEMT structures in the THz frequency range is proposed. In addition, the resonant electroluminescence signals are found intermixed with the THz emission caused by the hot electron transitions from conduction band to shallow donors as well as the black‐body radiation of heated AlGaN/GaN HEMT channel. It is found that the temperature increase of the conductive channel greatly suppressed the electroluminescence signal. Therefore, a proper cooling of the sample should be provided in advance.

High-Frequency and High-Power Performance of n-Type GaN Epilayers with Low Electron Density Grown on Native Substrate

“…Such a value corresponds to the activation energy of the silicon impurities in GaN material [ 18 , 28 ]. Note that similar energies were observed by THz electroluminescence spectroscopy of Si impurities in epilayers with and without HEMT structures [ 16 , 17 ].…”

“…However, if TDD is below 2 × 10 6 cm −2 and doping of the GaN epilayer is above 2 × 10 16 cm −3 , the numerical modelling shows that scattering on ionized impurities (at cryogenic temperatures) and on polar optical phonons (at room temperatures) dominates among other mechanisms that could limit the electron mobility [ 2 , 12 ]. Shallow impurities in GaN such as Si and O warrant type and quantity of dopants in the material, which define optical and electric properties of epilayers, and the characterization of which can be performed using various non-destructive methods [ 16 , 17 , 18 ]. The processes of impurity incorporation and resulting electronic and electric properties of the material have been efficiently investigated in A 3 B 5 semiconductors by applying density-functional theory calculations [ 19 , 20 , 21 , 22 ].…”