B. Adamowicz

XPS study of the L-CVD deposited SnO2 thin films exposed to oxygen and hydrogen

In this paper, the XPS study of SnO2 thin films deposited by the L-CVD technique are presented. The influence of exposition of the as-deposited samples to oxygen O2 and hydrogen H2 on their stoichiometry was determined. Moreover, on the basis of detailed shape analysis of the Sn3d5/2 and O1s XPS peaks, the chemical shift of binding energy corresponding to the change of sample stoichiometry was separated from a shift of the binding energy corresponding to the change of interface Fermi level position EF–Ev in the band gap, using a new procedure of deconvolution of the core level XPS peaks. The shift of the Sn3d5/2 peak by approximately 0.5 eV towards the lower binding energy after highest H2 exposure was interpreted as a true chemical shift due to an increase of Sn2+ component, whereas the shift of Sn3d5/2 peak and O1s peak after highest O2 exposure by approximately 0.5 eV towards the lower binding energy was interpreted as a result of the shift of the interface Fermi level position in the band gap towards the top of valence band at the surface, which corresponds to a deep accumulation layer typical for SnO2 thin films.

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...

Computer Analysis of Surface Recombination Process at Si and Compound Semiconductor Surfaces and Behavior of Surface Recombination Velocity.

A theoretical analysis of the surface recombination is performed for n-Si, GaAs and InP surfaces under photo-excitation in terms of the so-called effective surface recombination velocity Seff. A very strong dependence of Seff both on the excitation light intensity and the surface fixed charge density has been found. Seff reaches its maximum when ns≈ps, independently on the light intensity. Seff can be significantly reduced by shift of the surface Fermi level towards band edges by means of the surface fixed charge QFC or by appropriately reducing or reshaping the surface state density distribution.

Determination of the deep donor-like interface state density distribution in metal/Al2O3/n-GaN structures from the photocapacitance–light intensity measurement

We developed a method for determining of the deep donor-like interface state density distribution Dit(E) at the insulator/wide bandgap semiconductor interface in metal/insulator/semiconductor structures from the measurements of photocapacitance vs. ultraviolet light intensity CL(Φ). From the comparison of theoretical and experimental CL(Φ) curves we obtained the continuous donor Dit(E) in the energy range between 0.15 eV and 1 eV from the valence band top for a metal/Al2O3/n-GaN device. In addition, the acceptor-like interface state Dit(E) in the upper part of the bandgap was determined from the capacitance-voltage method.

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.

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

We determined the energy distribution of donor-like interface state density DitD(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 DitD(E) strongly decreasing from the value of 5×1013 to 4×1012 eV−1 cm−2 in the energy range between 0.12 eV and 0.45 eV from the AlGaN valence band edge.

Capacitance-voltage and photoluminescence study of high-k∕GaAs interfaces controlled by Si interface control layer

The authors performed a detailed capacitance-voltage (C-V) and photoluminescence (PL) study of the high-k dielectric/GaAs interface controlled by the Si interface control layer (Si ICL) grown by molecular beam epitaxy to investigate the feasibility of a PL method for interface characterization and to find out the optimum thickness of the Si ICL. The sample had a HfO2∕SiNx∕Si ICL/n-GaAs structure where the ultrathin SiNx buffer layer was formed by in situ partial nitridation of the Si ICL itself. For this structure, they measured the quantum efficiency of photoluminescence as a function of the excitation photon flux density and carried out a computer analysis to determine the most likely distribution of the interface state density Dit. Remarkably good agreements were obtained between the high-frequency C-V method and the PL method, indicating that the present PL method may serve as a powerful contactless and nondestructive tool for developing an optimal surface passivation structure and its processing tech...

Analysis of photoluminescence efficiency and surface recombination velocity of MBE-grown AlGaAs layers

Abstract Rigorous computer analysis of the band-edge PL efficiency ( I PL / Φ ) and the effective surface recombination velocity ( S eff ) was performed for n-Al 0.33 Ga 0.67 As surfaces versus the surface state density, N SS0 , in a wide range of photon flux density, Φ (from 10 12 to 10 25 cm −2 s −1 ). The behavior of electron ( E Fn ) and hole ( E Fp ) quasi-Fermi levels was also studied. In addition, the simulated I PL / Φ – Φ dependencies have been compared with experimental data for MBE-grown AlGaAs wafers passivated by ultrathin Si interface control layer.

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

We performed, for the first time, quantitative characterization of electron capture cross sections σ of the interface states at dielectric/III-N heterojunction interfaces. We developed a new method, which is based on the photo-assisted capacitance-voltage measurements using photon energies below the semiconductor band gap. The analysis was carried out for AlGaN/GaN metal-insulator-semiconductor heterojunction (MISH) structures with Al2O3, SiO2, or SiN films as insulator deposited on the AlGaN layers with Al content (x) varying over a wide range of values. Additionally, we also investigated an Al2O3/InAlN/GaN MISH structure. Prior to insulator deposition, the AlGaN and InAlN surfaces were subjected to different treatments. We found that σ for all these structures lies in the range between 5×10−19 and 10−16 cm2. Furthermore, we revealed that σ for dielectric/AlxGa1−xN interfaces increases with increasing x. We showed that both the multiphonon-emission and cascade processes can explain the obtained results.

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

The energy spectrum of interface state density, Dit(E), was determined at oxide/III-N heterojunction interfaces in the entire band gap, using two complementary photo-electric methods: (i) photo-assisted capacitance-voltage technique for the states distributed near the midgap and the conduction band (CB) and (ii) light intensity dependent photo-capacitance method for the states close to the valence band (VB). In addition, the Auger electron spectroscopy profiling was applied for the characterization of chemical composition of the interface region with the emphasis on carbon impurities, which can be responsible for the interface state creation. The studies were performed for the AlGaN/GaN metal-insulator-semiconductor heterostructures (MISH) with Al2O3 and SiO2 dielectric films and AlxGa1–x layers with x varying from 0.15 to 0.4 as well as for an Al2O3/InAlN/GaN MISH structure. For all structures, it was found that: (i) Dit(E) is an U-shaped continuum increasing from the midgap towards the CB and VB edges a...