Energy relaxations of hot electrons in AlGaN/AlN/GaN heterostructures grown by MOCVD on sapphire and 6H-SiC substrates

Abstract

Abstract. In this work, we investigated the hot-electron dynamics of AlGaN/GaN HEMT structures grown by MOCVD on sapphire and SiC substrates at 80 K. High-speed current-voltage measurements and Hall measurements over the temperature range 27-300 K were used to study hot-electron dynamics. At low fields, drift velocity increases linearly, but deviates from the linearity toward high electric fields. Drift velocities are deduced as approximately 6.55 × 10 6 and 6.60 × 10 6 cm/s at an electric field of around E ∼ 25 kV/cm for samples grown on sapphire and SiC, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, we used the so-called mobility comparison method with power balance equations. Although their low field carrier transport properties are similar as observed from Hall measurements, hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. We found that LO-phonon lifetimes are 0.50 ps and 0.32 ps for sapphire and SiC substrates, respectively. A long hot-phonon lifetime results in large nonequilibrium hot phonons. Non-equilibrium hot phonons slow energy relaxation and increase the momentum relaxation. The effective energy relaxation times at high fields are 24 and 65 ps for samples grown on sapphire and SiC substrates, respectively. They increase as the electron temperature decreases.

Energy Relaxation Rates in AlInN/AlN/GaN Heterostructures

“…3,8,9 Second, in a material where the momentum relaxation is dominated by ionized impurity, remote impurity, interface roughness, or optical phonon scattering , [8][9][10][11] electron temperatures can be determined as a function of the applied electric field by a simple comparison of the electric field-dependent and lattice temperaturedependent mobility curves. [8][9][10]12,13 Third, using the noise technique, the electron temperature can be estimated by measuring the electromagnetic radiation results of fluctuations in the electron velocities under high electric field. 14,15 Fourth, with the pump-probe Raman spectroscopy technique, the energy relaxation time can be directly determined from the decay of the anti-Stokes line intensity.…”

A 2015 perspective on the nature of the steady-state and transient electron transport within the wurtzite phases of gallium nitride, aluminum nitride, indium nitride, and zinc oxide: a critical and retrospective review

“…In 2011, Ilgaz et al [286] studied the energy relaxation of hot electrons within AlGaN/GaN/GaN heterostructures. Then, in 2012, Naylor et al [287] examined the steady-state and transient electron transport that occurs within bulk wurtzite GaN using an analytical band-structure that more accurately reflects the nature of the actual band-structure.…”

Temperature dependent energy relaxation time in AlGaN/AlN/GaN heterostructures

“…In degenerate and non-degenerate material, where the momentum relaxation is dominated by ionized impurity, remote impurity, interface roughness, or optical phonon scattering [3,5,6,9], electron temperatures as a function of the applied electric field can be determined as a function of the applied electric field by a simple comparison of the electric field dependent and lattice temperature dependent mobility curves [5,6,[9][10][11].…”

“…Comparatively little work has been published in the literature concerning measurements of the power loss of hot electrons in material systems, where the 2D electron gas is confined in GaN-based systems. Most reports in the literature obtain hot electron energy relaxation in GaN systems from the analysis of the amplitude variation of quantum oscillations [12][13][14][15] and mobility [10,11] with an electric field and temperature, fluctuations in the electron velocities under the high electric field [4,16], and decay of the anti-stokes line intensity [17].…”

“…An expression for the power loss due to optical phonon emission and absorption can be written [10,11] in the form:…”