Modelling of Polarization Charge-Induced Asymmetry of I-V Characteristics of AlN/GaN-Based Resonant Tunnelling Structures

Abstract

PACS: 73.40.Gk; 73.61.Ey Numerical simulations of AlN/GaN-based resonant tunnelling diode structures are presented, employing self-consistent real-time Green's functions. The simulated current-voltage characteristics show strong asymmetry effects due to polarization charges at the heterointerfaces in the doublebarrier region.Introduction During the last decade there has been tremendous progress in semiconducting III-nitride material science and technology. Early, very successful device applications in the field of optoelectronics (blue LEDs and laser diodes) and power microelectronics (HEMTs) have further driven the improvement of the materials and in turn of the devices. Even though the nitrides are far from the level of perfection seen in the technology of GaAs, the next natural step is towards quantum devices. In this sense, the resonant tunnelling diode (RTD) is an attractive candidate and offers the possibility of fundamental investigations of quantum phenomena as well as for modern device applications. Up to now, little attention has been paid to these types of structures and their functionality, when realized on the basis of nitride semiconductors.Kikuchi et al. [1] were the first to report the successful fabrication of RTDs based on AlN/GaN double-and multi-quantum well structures. The typical negative differential resistance (NDR) region in the current-voltage (I-V) characteristic was clearly observed, and, interestingly, a strong asymmetry was revealed: the NDR was only measured for one bias polarity and not for the opposite one (at least in the voltage range investigated). Due to the polarization charges built up at the wurtzite nitride heterojunctions, opposite electric fields are induced in the barrier and well regions of the device, which obviously are related to the observed asymmetry. Previous model calculations of GaNbased RTD structures showed that the effect of polarization fields is to shift the resonances in the transmission probability in comparison to the same hypothetical structure without polarization fields [2]. The model presented here goes a step further and deals with the self-consistent calculation of the current across the device structure under nonequilibrium conditions. This provides a direct comparison with the experiment and we are able to reproduce the measured asymmetry of the I-V characteristics.

AlN/GaN double-barrier resonant tunneling diodes grown by metal-organic chemical vapor deposition

“…The observed asymmetry of the I-V characteristics with respect to the applied voltages was caused by an asymmetry of the barrier structure caused by the polarization charges at the heterointerfaces in the DB region. 16,17 These charges also led to NDR for one bias polarity and not for the opposite one, in harmony with the theory 17 and our observations. 7,8 Figure 4 inset displays the simulated 12 schematic conduction band diagram of DB active layer.…”

Resonance and current instabilities in AlN/GaN resonant tunnelling diodes

“…This modiÿes considerably the potential proÿle of the double barrier structure. To understand the e ect of polarisation charges on the potential proÿle of the RTD structures, self-consistent simulations of the conduction band proÿle were obtained using a model based on real-time tight-binding Green's functions [5], the details will be published elsewhere. This model suggests that a resonance will only be observed in reverse bias when the occupied states in the emitter layer coincide with the energy of the ÿrst excited quasi-bound level in the quantum well, because the ground state in the QW is located below the Fermi level in the emitter.…”

“…Recently, Kikuchi et al, have reported resonant tunnelling in GaN/AlGaN double barrier resonant tunnelling diodes (RTDs) [1][2][3] and theoretical models for resonant behaviour in such structures have been discussed [4,5]. However, Kikuchi et al, concluded that this was conventional resonant tunnelling behaviour based on measurements in one direction of current-voltage (I (V )) sweep only [1][2][3].…”

Effects of substrate quality and orientation on the characteristics of III-nitride resonant tunneling diodes

“…Such internal electric fields can lead to highly asymmetric I-V characteristics. 21,22 Thus, one way to improve the NDR characteristics of DB RTDs is by minimizing these polarization fields by growing the RTDs on nonpolar substrate orientations. The recent commercial availability of low dislocation density (10 6 cm -2 ) nonpolar m-plane orientation FS-GaN substrates 6 enables studying the effects of polarization on the NDR of low Al content (10%) DB RTDs.…”