Direct measurement of donor-like interface state density and energy distribution at insulator/AlGaN interface in metal/Al₂O₃/AlGaN/GaN by photocapacitance method

Abstract

We determined the energy distribution of donor-like interface state density D-itD(E) at the Al2O3/AlGaN interface in a metal/Al2O3/AlGaN/GaN heterostructure (MISH) capacitor. In this order, we developed a point-by-point graphical method based on the measurement and simulations of the MISH photocapacitance versus ultraviolet light intensity. We found a tail-like shaped D-itD(E) strongly decreasing from the value of 5 x 10(13) to 4 x 10(12) eV(-1) cm(-2) in the energy range between 0.12 eV and 0.45 eV from the AlGaN valence band edge. (C) 2013 AIP Publishing LLC

Characterization of capture cross sections of interface states in dielectric/III-nitride heterojunction structures

“…The calculated C-V curves were obtained from a numerical solution of the Poisson's equation by finite element method with Neumann boundary conditions at the interfaces, i.e., insulator/AlGaN and insulator/InAlGaN as well as AlGaN/GaN and InAlGaN/GaN, which were determined by D it ðEÞ and fixed charge density originating from spontaneous and piezoelectric polarization. 14,15 The calculation reproduced well the measured C-V characteristics, which is an independent confirmation of the reliability of the developed method. It should be noted that in the described method, it is necessary to use a sufficiently high light intensity for the sample illumination in order to obtain full depopulation of the probed interface states corresponding to the saturation of the DV th and thus avoiding a possible random increase of DV th vs. T. In addition, in the case of D it ðEÞ which cannot be approximated by the straight line, one can use a polynomial fitting.…”

“…[10][11][12][13][14][15][16] As a consequence, there is still a lack of understanding of interface state fundamental properties at dielectric/III-N heterojunction interfaces, especially their dynamic trapping/emitting behavior expressed in terms of capture cross sections. Furthermore, it should be noted that, as a matter of fact, there is just only one report 17 about the values of the capture cross section for dielectric/ III-N heterojunction interfaces.…”

On the origin of interface states at oxide/III-nitride heterojunction interfaces

“…The details of the measurement process can be found elsewhere. 18,19 The values of V accum G and V depl G for the examined structures are shown in Table I. Furthermore, in Table I we summarized the values of the spillover-voltage (V Go ) (where 2DEG electrons spill over the barrier accumulating at the oxide/barrier interface) and the threshold voltage (V th ) in C-V curves.…”

“…It should be noted that due to the negligible electron concentration (n) at the insulator/barrier interface, the non-radiative recombination through the interface states is totally reduced. 18,19 However, the excess carriers can recombine radiatively through band-to-band transitions with a rate Bnp (where B is the band-to-band recombination coefficient and p is the photohole concentration) and non-radiatively through defects by the Shockley-Read-Hall (SRH) mechanism 30 at a rate U SRH . The model equations are based on the 1D Poisson's equation and current continuity equations in a semiconductor layer and Laplace's equation in the insulator layer.…”

“…[13][14][15] However, the electronic states existing at such interfaces may significantly influence the device performance due to uncontrolled interface charging. [16][17][18][19][20][21][22][23] Despite the high importance of interface states at dielectric/III-N heterojunction interfaces, their origin and properties, in particular, the density distribution vs. energy, D it (E), in the wide band gap, E G , and charge type (donor-like or acceptor-like) are still not clarified. The main reason of such a situation are the extreme obstacles in the quantitative characterization of interface states by means of the electrical methods in the case of III-N heterojunction based devices because of the presence of two interfaces and very long time constants for charge emission from the deep states at room temperature (RT).…”