Polar Optical Phonon Instability and Intervalley Transfer in Gallium Nitride
- PDF / 344,390 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 95 Downloads / 262 Views
Abstract We develop a simple, one-dimensional, analytical model, which describes electron transport in gallium nitride. We focus on the polar optical phonon scattering mechanism, as this is the dominant energy loss mechanism at room temperature. Equating the power gained from the field with that lost through scattering, we demonstrate that beyond a critical electric field, 114 kV/cm at T = 300 K, the power gained from the field exceeds that lost due to polar optical phonon scattering. This polar optical phonon instability leads to a dramatic increase in the electron energy, this being responsible for the onset of intervalley transitions. The predictions of our analytical model are compared with those of Monte Carlo simulations, and are found to be in satisfactory agreement.
Introduction Gallium nitride ( GaN ) has long been recognized a promising candidate for semiconductor device applications [1, 2]. While initial efforts to research this material were hindered by growth difficulties, recent improvements in material quality has allowed for the realization of GaN based devices. In particular, GaN lasers [3] and high performance transistors [4] have been fabricated. These developments have fueled considerable interest in GaN. In order to analyze and improve the design of GaN based devices, a thorough understanding of electron transport in this material is necessary. Thus far, the steady-state velocity-field characteristics of GaN have been the primary focus of investigation [5, 6, 7, 8, 9, 10]. In Figure 1, we plot the velocity-field characteristic associated with GaN, for the temperature set to 300 K and the doping concentration set to 1 X 1017 cm- 3 [11]. We see that while the drift velocity increases monotonically at low fields, it achieves a maximum of 2.9 x 107 cm/s at 140 kV/cm, beyond which the drift velocity diminishes with further increases in the applied field. This negative differential conductivity is attributable to intervalley transitions, the upper valley electrons being 'heavier', and thus 'slower', than their lower valley counterparts. In this paper, we demonstrate that a polar optical phonon instability is responsible for the onset of these intervalley transitions. In particular, adopting a simple, one-dimensional model, which focuses on polar optical phonon scattering, we demonstrate that beyond a certain critical field that the power gained from the applied field exceeds that lost due 549 Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society
33
I
I
S2. 4
009900000000000000000
0
S0
0
1000
500
Electric Field ( kV/cm) Figure 1: The velocity-field characteristic of GaN. This result was obtained from Monte Carlo simulations of electron transport. to polar optical phonon scattering, i.e., a polar optical phonon instability occurs and the electron energy increases dramatically. We then use this model to predict at what electric field intervalley transitions begin to occur in GaN. We demonstrate that our theoretical predictions are consistent with results of Monte Carlo simula
Data Loading...
