Admittance of p-n junctions containing traps

Journal of Applied Physics

2001

The effect of the deep acceptor Mg on the electrical characteristics of p-doped GaN Schottky diodes is analyzed. The theoretical study is based on the numerical resolution of the basic semiconductor equations, including the continuity equation for the Mg-related acceptor level. It gives the steady-state and small-signal analysis of p-doped GaN:Mg Schottky diodes, yielding as final result the frequency dependent capacitance and conductance of the structure. It is shown that the low-frequency characteristics are determined by the carrier exchange between the Mg related impurity level and the valence band, whereas above the impurity transition frequency, the hole modulation of the depletion layer edge governs the electrical response. Detailed results are shown on the effect of temperature, applied steady-state voltage and series resistance. The study of two back-to-back connected GaN Schottky diodes reveals the appearance of typical features in the electrical characteristics, depending on the respective Schottky barrier height of the two junctions.

Section: Introductionsupporting

confidence: 73%

Section: A Schottky Gan:mg Junction Under Room Temperature Zero-biamentioning

confidence: 99%

Competition between deep impurity and dopant behavior of Mg in GaN Schottky diodes

Journal of Applied Physics

2001

“…Let us first discuss the behaviour of the system at room temperature. The existence of a cut-off frequency in capacitance curves of such shape, associated with the presence of a peak in the frequency dependence of G/ω, is usually related to the presence of a deep level in the layer [5]. At low frequencies, deep states, which are involved in transitions with either the valence or the conduction band, follow the modulation of the applied voltage, yielding the plateau regime in the capacitance.…”

Section: Resultsmentioning

confidence: 99%

“…The position of the main peak in the G/ω-versus-frequency curve at room temperature can be related to the cut-off frequency of an RC series circuit which is given here by (2πRSCtot) -1 , where Ctot is the total equivalent capacitance of the two junctions, including the contributions of deep impurities, and RS is given by the high-frequency regime of the real part of the impedance. The variation of this peak with temperature is not only due to the temperature dependence of RS but also of the defect capacitances [5].…”

Section: Fig 2 Real (A) and Imaginary (B) Part Of Impedance Z Versumentioning

confidence: 94%

Experimental and theoretical investigations of the electrical properties of undoped and magnesium-doped GaN layers

Journal of Crystal Growth

et al. 2001

The ac characteristics of GaN : Mg and undoped GaN layers, grown by MOVPE on sapphire substrates, are measured for a wide range of temperature and bias conditions, in order to investigate the effect of the magnesium-related level on the transport properties. Two peaks, whose height and position depend on the measurement temperature, are observed in the admittance curves (G/ω versus frequency) of the Mg-doped samples, whereas only one peak appears in undoped samples. The study of the frequency dependence of the impedance, with a model including the two metallic Au/GaN junctions, the GaN layer itself, shows that, besides the effect of the differential resistance of the layer which plays a role in both sample types, the presence of a Mgrelated deep level contributes to the observed variations of the peaks in the admittance curves of the p-doped samples. Results of a theoretical steady-state and small-signal analysis based on numerical modelling of the Au/ GaN/Au heterostructure complete our analysis.

“…But doing so even in the case of deep impurities, at concentrations lower than that of the shallow dopant, several terms given in the expression of the transition frequency are neglected. 31 This approximation is even worse in the case of Mg-doped GaN, where Mg is at an energy level which simultaneously acts as a dopant and deep impurity.…”

Section: Admittance Curves Of the Back To Back Connected Schottky mentioning

confidence: 99%

Thermal admittance spectroscopy of Mg-doped GaN Schottky diodes

Journal of Applied Physics

et al. 2001

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.