Thermal admittance spectroscopy of Mg-doped GaN Schottky diodes

Abstract

Thermal admittance spectroscopy measurements at temperatures ranging from room temperature to 90 K are performed on Schottky structures based on Mg-doped GaN layers grown by metalorganic vapor phase epitaxy on sapphire. The analysis of the experimental data is made by a detailed theoretical study of the steady-state and small-signal electrical characteristics of the structures. Numerical simulations are based on the solution of the basic semiconductor equations for the structure consisting of two Schottky diodes connected back to back by a conduction channel formed by the GaN layer. The description explicitly includes the Mg-related acceptor level, with its temperature-and position-dependent incomplete occupation state, leading to a dynamic exchange with the valence band. It fully reproduces the variations with temperature of the capacitancefrequency and conductance over frequency curves, allowing to give for all temperature ranges the origin of the various contributions to the junction capacitance and of the microscopic mechanisms responsible for the capacitance-frequency cutoff. Series resistance effects are shown to be dominant at temperatures above 230 K, whereas the Mg-related acceptor level governs the electrical behavior below 230 K. The existence of a second acceptor level with an activation energy of several tens of meV is revealed from the analysis of the characteristics at low temperature. An optimized fitting procedure based on the comparison of the electrical characteristics obtained from the numerical simulations to the experimental data allows one to determine the microscopic parameters describing the structure, among which the acceptor activation energies, thermal capture cross sections, concentrations, and the Schottky contact barrier heights are the most important ones. The obtained activation energy of the Mg-acceptor level of 210 meV is by a factor of 2 larger than that obtained from a classical Arrhenius plot, showing that a complete description of Mg-doped GaN junctions requires the correct treatment of the Mg level, acting as a dopant and as deep impurity, as well as the inclusion of series resistance effects.

Effect of copper phthalocyanine (CuPc) interlayer on the electrical characteristics of Au/n-GaN Schottky rectifier

“…However the current across an interface with numerous spatial fluctuations depends exponentially on barrier height and the ability of a current to flow preferentially through barrier minima, resulting in an underestimation of barrier height extracted from I-V methods [31]. The capacitance measurement is one of the most important methods for obtaining information on the interface of the Schottky contacts and can provide the required accuracy in determining the variation of the interface state capacitance as a function of the forward bias at low frequency [32][33][34][35][36]. Based on the Hill-Coleman method [37], the N SS can be determined by the following relation:…”

Electrical Characterization of InGaN/GaN Multiple‐Quantum‐Well Structures by Thermal Admittance Spectroscopy

“…Although one should be careful when using such a method [8], this type of analysis has been applied to QW structures, either to assess the presence of defects [9] or to determine QW parameters [10]. The Arrhenius plot of the cutoff frequencies corresponding to the five RC series circuits, shown in Fig.…”

“…The obtained values of the activation energies cover a large range, which may be an indication of the existence of discrepancies in the composition of the InGaN alloy or in geometrical parameters of the QWs. Further investigations, based on the solution of the basic semiconductor equations [8] for the ELT structure, are being performed in order to clarify the microscopic origin of the activation energies. …”

The Properties of p-GaN with Different Cp2Mg/Ga Ratios and Their Influence on Conductivity

“…Thus, further investing the growth parameter on the properties of p-GaN is important for us to realize high conductivity p-GaN. However, p-GaN is difficult to obtain high conductivity owing to high Mg activation energy, reportedly in the range of 120-250 meV, [1][2][3][4] the compensation of deep donors, and the limited solubility of Mg in GaN. [5][6][7] Especially, the compensation phenomenon is very important to determine the conductivity in p-GaN.…”