Marcin Miczek

Effects of interface states and temperature on the C-V behavior of metal/insulator/AlGaN/GaN heterostructure capacitors

The impact of states at the insulator/AlGaN interface on the capacitance-voltage (C-V) characteristics of a metal/insulator/AlGaN/GaN heterostructure (MISH) capacitor was examined using a numerical solver of a Poisson equation and taking into account the electron emission rate from the interface states. A parallel shift of the theoretical C-V curves, instead of the typical change in their slope, was found for a MISH device with a 25-nm-thick AlGaN layer when the SiNx/AlGaN interface state density Dit(E) was increased. We attribute this behavior to the position of the Fermi level at the SiNx/AlGaN interface below the AlGaN valence band maximum when the gate bias is near the threshold voltage and to the insensitivity of the deep interface traps to the gate voltage due to a low emission rate. A typical stretch out of the theoretical C-V curve was obtained only for a MISH structure with a very thin AlGaN layer at 300 °C. We analyzed the experimental C-V characteristics from a SiNx/Al2O3/AlGaN/GaN structure me...

Capacitance–Voltage Characteristics of Al2O3/AlGaN/GaN Structures and State Density Distribution at Al2O3/AlGaN Interface

The potential modulation and interface states of Al2O3/Al0.25Ga0.75N/GaN structures prepared by atomic layer deposition (ALD) were characterized by capacitance–voltage (C–V) measurements. We observed the peculiar C–V characteristics with two capacitance steps in forward and reverse bias regions, corresponding to the electron accumulation or depletion behavior at the Al2O3/AlGaN and AlGaN/GaN interfaces. From the experimental and calculated C–V characteristics, it was found that the charging and discharging of interface states near the AlGaN conduction-band edge mainly caused the stretch-out and hysteresis of the C–V curve at the forward bias. On the other hand, it is likely that the interface states near the midgap or deeper in energies act as fixed charges. From the bias-dependent hysteresis voltage in the forward bias region and the photo-induced voltage shift at the reverse bias, we estimated the interface state density distribution at the Al2O3/AlGaN interface for the first time. The present ALD-Al2O3/AlGaN/GaN structure showed relatively high interface state densities with a minimum density of 1×1012 cm-2 eV-1 or higher.

Simulations of Capacitance–Voltage–Temperature Behavior of Metal/Insulator/AlGaN and Metal/Insulator/AlGaN/GaN Structures

The effect of electronic states at insulator/AlGaN and AlGaN/GaN interfaces on capacitance–voltage (C–V) characteristics of a metal/insulator/semiconductor (MIS) capacitor with an AlGaN layer and a metal/insulator/semiconductor heterostructure (MISH) with an AlGaN/GaN heterojunction was studied theoretically taking into account extremely slow electron emission from the deep interface levels. The states at the insulator/AlGaN interface in MIS and at the AlGaN/GaN interface in MISH stretch out the C–V curves as usual, whereas the insulator/AlGaN interface states in MISH only shift the characteristics at room temperature and 300 °C (fixed-charge-like behavior). These effects were explained by the different positions of the Fermi level at the studied interfaces. Theoretical C–V curves were compared with experimental characteristics, which are available in the literature, measured at room and higher temperatures by the authors and others.

Impact of Interface States and Bulk Carrier Lifetime on Photocapacitance of Metal/Insulator/GaN Structure for Ultraviolet Light Detection

The influence of interface state density and bulk carrier lifetime on the dependencies of photocapacitance versus wide range of gate bias (-0.1 to -3 V) and light intensity (109 to 1020 photon cm-2 s-1) was studied for metal/insulator/n-GaN UV light photodetector by means of numerical simulations. The light detection limit and photocapacitance saturation were analyzed in terms of the interface charge and interface Fermi level for electrons and holes and effective interface recombination velocity. It was proven that the excess carrier recombination through interface states is the main reason of photocapacitance signal quenching. It was found that the photodetector can work in various modes (on–off or quantitative light measurement) adjusted by the gate bias. A comparison between experimental data and theoretical capacitance-light intensity characteristics was made. A new method for the determination of the interface state density distribution from capacitance–voltage-light intensity measurements was also proposed.

UV-Induced Variation of Interface Potential in AlOx/n-GaN Structure

We performed a feasibility study of UV detection using an AlOx/n-GaN structure. The AlOx layer was deposited on n-GaN using diethyl aluminum ethoxide as a precursor. We obtained a refractive index of 1.59, a bandgap of 7.0 eV, and an oxygen composition of 1.48 for the AlOx layer. Even at higher temperatures, no significant change appeared in the capacitance–voltage curves, which were close to the ideal curve, indicating well-controlled and stable interface properties. From the photo response measurements, pronounced variation of the interface potential at the AlOx/GaN interface was observed under UV illumination, which was independent of temperature. The gate bias systematically modulated the depth of the interface potential well and thereby the density of accumulated holes resulting from UV illumination. The AlOx/GaN structure is sensitive to flame with a low power density.

Rigorous analysis of the electronic properties of InP interfaces for gas sensing

Abstract A theoretical analysis of the surface Fermi level position ( E FS ) at n-InP interfaces with different surface state density ( N SS ( E )) and surface fixed charge ( Q FC ) representing adsorbed ions or surface δ-doping has been performed in order to understand the InP-based gas sensor behaviour. Furthermore, the in-depth profiles of the potential barrier in equilibrium and under illumination (surface photovoltage) have been rigorously calculated. A U-shaped interface state continuum has been assumed in accordance with the Disorder Induced Gap State model. From the simulated dependencies of E FS vs. the minimum surface state density N SS0 , the movement of E FS in the energy band gap as well as its pinning position have been investigated. In addition, the analysis of the E FS sensitivity to the negative and positive Q FC has revealed the remarkable charge detection sensitivity of InP interfaces within different dynamic ranges.

Electronic properties of AlxGa1−xAs surface passivated by ultrathin silicon interface control layer

Abstract The photoluminescence surface state spectroscopy (PLS3) method was applied to a study of the surface state distribution (NSS), effective surface recombination velocity (Seff), electron (EFn) and hole (EFp) quasi-Fermi levels and band bending (VS) on the Al0.33Ga0.67As surface air-exposed and passivated by the Si interface control layer (ICL) technique. Using the detailed measurements of the PL quantum efficiency for different excitation intensities, combined with the rigorous computer simulations of the bulk and surface recombination processes, the behavior and correlation among the surface characteristics under photo-excitation was determined. The present analysis indicated that forming of a Si3N4/Si ICL double layer (with a monolayer level control) on AlGaAs surface reduces the minimum interface state density down to 1010 cm−2 eV−1 and surface recombination velocity to the range of 104 cm/s under low excitations.