Energy Relaxation by Warm Two-Dimensional Electrons in a GaN/AlGaN Heterostructure

Abstract

The rate of energy loss per electron, P e , by a two-dimensional electron gas in an GaN/AlGaN heterostructure has been measured as a function of electron temperature, T e , in the range 0.4-35 K. A combination of zero and high magnetic field electrical transport measurements were used to determine T e as a function of the power dissipated in the device. It was found that P e / T n e , with n % 5 at the lowest temperatures, T e ( 2 K, while for higher temperatures, T e > 10 K, n ! 1. The experimental results are compared with numerical calculations of the energy relaxation rate. In the range of temperatures studied, emission of piezoelectrically coupled acoustic phonons was found to be the dominant energy relaxation mechanism.Introduction The process of hot carrier energy relaxation is of fundamental importance to the performance of all semiconductor electronic and optoelectronic devices. Measurement of energy relaxation rates provides information about the electron-phonon interaction which is of use in modelling device behaviour. Energy relaxation by hot two-dimensional (2D) carriers has been extensively studied in GaAs heterojunctions and quantum wells and Si MOS devices [1]. However, to date, there has been much less work with the aim of examining this process in GaN and its alloys.Recently Lee et al. [2] have reported measurements of the energy relaxation by warm 2D electrons in a GaN/AlGaN heterojunction. The temperature dependence of the amplitude of Shubnikov-de Haas (SdH) magnetoresistance oscillations was used as a thermometer for the electron temperature, T e . However, these measurements were limited by the technique to the electron temperature range T e < 4 K. Stanton et al. [3] studied the energy relaxation rate in bulk (3D) GaN samples using zero-field transport measurements to determine T e . In the low mobility samples used, this technique was applicable to a wide range of electron temperature, 1.5 K < T e < 300 K. However, in higher mobility samples, where phonon scattering makes a significant contribution to the mobility in the temperature range of interest, the technique must be used with caution [4].The main aim of the work described in this paper was to use the zero-field transport techniques to extend the measurements of Lee et al. to higher electron tempera-

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

“…6. The electron temperature dependence of the power loss was found to be different than the previous reports on energy relaxation by hot electrons [12][13][14][15] in GaN/AlGaN heterojunctions. Since the layer structures and doping parameters of all the investigated samples are identical, the observed variations in power loss may be associated with the differences in the mobility of the samples (see Eq.…”

“…These trends remain at all electron temperatures in the range of 1.8-8 K. This result is also in accord with the fitting outcome of the Eq. (5) and other researchers' results in AlGaN/GaN heterojunctions [12][13][14][15].…”

“…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].…”

Energy relaxation probed by weak antilocalization measurements in GaN heterostructures

“…In the B-G regime, the e-p interaction is expected to have various power-law dependences on temperature. [5][6][7][8][12][13][14] For example, the phonon emission via piezoelectric coupling leads to T e 5 and T e 3 dependence for energy relaxation with and without static screening, and the phonon emission via deformation potential leads to T e 7 and T e 5 dependence with and without static screening. 15 At low temperature, it is believed that the piezoelectric coupling is the dominating energy relaxation mechanism in the GaN system.…”

“…15 At low temperature, it is believed that the piezoelectric coupling is the dominating energy relaxation mechanism in the GaN system. [5][6][7][8] The electron screening effect of local potential must be included in the calculations of energy relaxation rates. At very low temperature, when the wavelength of the emitted phonons becomes comparable to the mean free path of the electrons, the static screening is no longer suitable to describe the system.…”