High temperature electrical transport properties of MBE-grown Mg-doped GaN and AlGaN materials

Abstract

This paper discusses the results of high temperature resistivity and Hall effect studies of Mg-doped GaN and Al x Ga 1-x N epilayers (0.05<x<0.23). The studied samples were grown by molecular beam epitaxy (MBE) on low temperature buffers of GaN and AlN deposited on sapphire substrate. The experiments were carried out at temperatures ranging from 300 up to 1000 K. Up to certain critical temperature T C (around 800 K) a typical increase of the conduction processes due to the excitation of impurity states has been observed with an activation energy of about E A = 200 meV. However, at this critical temperature T C , an annealing effect was observed in all the investigated samples. At this critical temperature, the increase of the free carrier concentration as a function of time leads to an irreversible decrease of the samples resistivity of more than 60 %. The observed temperature dependences of the electrical transport properties are analysed in the frame of an impurity model including shallow donors and Mg-related acceptors (with E A ~ 200 meV). In some cases, an additional conduction channel not related to the free carriers in the valence band must be taken into account. This can lead to an incorrect determination of hole concentration in valence band, important parameter in the process of radiative recombination.

p-type conductivity in GaN:Zn monocrystals grown by ammonothermal method

“…In this way, an impurity band of the finite width is formed and holes can hop between different impurity atoms. A similar observation of hopping conductivity at relatively high temperature was published in the case of heavily Mg-doped epitaxial layers [8,26,27]. In region C, this mechanism dominated the conduction process.…”

“…Theoretical pv at RT is also given. For benchmarking purpose literature data for GaN:Mg are provided[26,27,34] in the last column (NA-NDeffective density of acceptors, EMgionization energy of Mg acceptor).…”

Low‐Temperature Electrical Transport Properties of Molecular Beam Epitaxy‐Grown Mg‐Doped GaN Subjected to a High‐Temperature Annealing Process

“…It was pointed out that annealing in an ambient nitrogen environment between 870 and 1120 K for one hour led to no change in the electrical properties of the material grown by reactive MBE with ammonia. [ 6 ] However in our previous work, [ 7 ] from the electrical transport measurements carried out in the temperature range from 300 K up to 1000 K, we showed that for temperatures T exceeding some critical value T C ≥ 800 K, the resistivity ρ and Hall concentration p H became time‐dependent. After the annealing process, a more than ≈60% irreversible decrease of the sample resistivity as well as an increase of the free hole concentration has occurred.…”

“…The crystal growth procedure was the same as the one applied to the samples in the previous study. [ 7 ] The materials under study were grown on 2 inch c‐plane (0001) sapphire substrates by MBE in a “Riber 32 P” reactor. Effusion cells were used for Ga and Al elements, the Mg dopant was supplied by a RIBER VCOR110 valved cell and ammonia (NH 3 ) was used as the nitrogen source.…”

Recent Progress on Aluminum Gallium Nitride Deep Ultraviolet Lasers by Molecular Beam Epitaxy

“…In this regard, significant efforts have been devoted to growing highly conductive p-type AlGaN epilayers with high Al contents by MBE. [79][80][81]131,132] Although the polarization and superlattice (SL) doping methods have also been studied intensively and devices using these approaches have also been demonstrated, [23,[133][134][135][136] in what follows we shall focus on the state-of-the-art p-type conduction from p-type AlGaN epilayers by Mg doping.…”