Interface State Density Distribution Research Articles

Room temperature photoluminescence studies of nitrided InP(100) surfaces

The evolution of thin InN overlayer grown on InP (100) rich In substrate was investigated at room temperature by photoluminescence method versus the duration of nitridation process. The main important parameters were the duration of the process, and the angle of the reactive nitrogen flow. The nitridation was performed by a glow discharge source (GDS). The correlations between the electronic properties, gathered from photoluminescence (PL) measurements, and the chemical composition of InN–InP interfaces, derived from Auger electron spectroscopy (AES) were found. AES revealed that the nitridation process proceeds quickly in time showing self-limiting behavior. It is more effective for grazing nitrogen flux. The interface state density distributions, N SS( E), were determined via advanced computer-aided analysis of dependencies of band edge PL efficiency, Y PL, versus excitation light intensity, Φ. The analysis showed that the substrates were well passivated with N SS( E) minima on the order of 5·10 11 cm − 2 eV − 1 . The nitrogen flux angle during the nitridation was found to have an influence on Y PL( Φ) spectra. In all analyzed cases the grazing nitrogen flux generated the interface with slightly improved N SS( E) distribution. Finally, the behavior of Y PL versus Φ and N SS( E) was precisely examined.

Current transport mechanism in Al/Si 3N 4/p-Si (MIS) Schottky barrier diodes at low temperatures

The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of metal–insulator–semiconductor (Al/Si 3N 4/p-Si) Schottky barrier diodes (SBDs) were measured in the temperature range of 80–300 K. By using the thermionic emission (TE) theory, the zero-bias barrier height Φ B0 calculated from I– V characteristics was found to increase with increasing temperature. Such temperature dependence is an obvious disagreement with the negative temperature coefficient of the barrier height calculated from C– V characteristics. Also, the ideality factor decreases with increasing temperature, and especially the activation energy plot is nonlinear at low temperatures. Such behaviour is attributed to Schottky barrier inhomogeneties by assuming a Gaussian distribution of barrier heights (BHs) at interface. We attempted to draw a Φ B0 versus q/2 kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of Φ Bo = 0.826 eV and α o = 0.091 V for the mean barrier height and standard deviation at zero-bias, respectively, have been obtained from this plot. Thus, a modified ln( I o/ T 2) − q 2 σ o 2/2( kT) 2 versus q/ kT plot gives Φ B0 and Richardson constant A * as 0.820 eV and 30.273 A/cm 2 K 2, respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273 A/cm 2 K 2 is very close to the theoretical value of 32 A/cm 2 K 2 for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I– V characteristics of the Al/Si 3N 4/p-Si Schottky barrier diodes can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. In addition, the temperature dependence of energy distribution of interface state density ( N SS) profiles was determined from the forward I– V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.

Current transport in Zn/p-Si(1 0 0) Schottky barrier diodes at high temperatures

In this study, we have performed behavior of the non-ideal forward bias current–voltage ( I–V) and the reverse bias capacitance–voltage ( C–V) characteristics of Zn/p-Si (metal–semiconductor) Schottky barrier diode (SBDs) with thin interfacial insulator layer. The forward bias I–V and reverse bias C–V characteristics of SBDs have been studied at the temperatures range of 300–400 K. SBD parameters such as ideality factor n, the series resistance ( R S) determined Cheung's functions and Schottky barrier height, Φ b , are investigated as functions of temperature. The ideality factor n and R S were strongly temperature dependent and changed linearly with temperature and inverse temperature, respectively. The zero-bias barrier heights Φ b 0 ( I – V ) calculated from I–V measurements show an unusual behavior that it was found to increase linearly with the increasing temperature. However, the barrier height Φ b ( C – V ) calculated from C–V measurements at 500 kHz frequency decreased linearly with the increasing temperature. The correlation between Φ b 0 ( I – V ) and Φ b ( C – V ) barrier heights have been explained by taking into account ideality factors n and the tunneling factor ( α χ 1 / 2 δ ) in the current transport mechanism. Also, the temperature dependence of energy distribution of interface state density ( N SS ) was determined from the forward I–V measurements by taking into account the bias dependence of the effective barrier height. The higher values of n and R S were attributed to the presence of a native insulator on Si surface and to high density of interface states localized at semiconductor–native oxide layer (Si/SiO 2) interface.

The energy distribution of the interface state density of SnO 2/p-Si (1 1 1) heterojunctions prepared at different substrate temperatures by spray deposition method

We have fabricated the Al/SnO 2/p-Si (1 1 1) Schottky diodes having the SnO 2/p-Si heterojunction prepared using the spray deposition process at various Si substrate temperatures and report the first investigation of the energy distribution of the interface state density of these diodes. The barrier height Φ B estimated from the I– V and C– V measurements agrees with each other and increased with increasing substrate temperature. The energy distribution of interface state density N ss was determined from the forward bias I– V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density N ss of the diodes has an exponential growth with bias from the midgap towards the top of the valance band for each diode; for example, from 1.46 × 10 12 eV −1 cm −2 in (0.46 − E v) eV to 1.29 × 10 12 eV −1 cm −2 in (0.53 − E v) eV for SD3 sample.

Comparison of interfaces states density through their energy distribution and LVSILC induced by uniform and localized injections in 2.3 nm thick oxides

Experiments were performed on 2.3 nm thin gate oxides. The interface state density and the low voltage stress induced leakage current are compared after uniform and localized stresses. The energy distribution of interface state density in the bandgap is then determined. The normalized variations of interface state density and gate leakage current are shown to be comparable after localized stress but completely different after uniform stresses.

Charge trapping and interface characteristics of thermally evaporated HfO2

Charge trapping and interface characteristics of hafnium oxide (HfO2) films, grown by standard thermal evaporation, were investigated. High frequency capacitance–voltage and conductance measurements were carried out at various temperatures on aluminum gate metal–oxide–semiconductor capacitors, annealed at 450°C. A hysteresis below 30mV was observed. Electrical data show, that charge trapping in HfO2 initially increases with decrease in temperature while it shows a turnaround phenomenon when the temperature is decreased further. Interface state density distribution observed at low temperatures suggests that charge-trapping behavior of these films is mostly due to shallow traps at the interface.

The importance of the neutral region resistance for the calculation of the interface state in Pb/p-Si Schottky contacts

We have fabricated H-terminated Pb/p-type Si Schottky contacts with and without the native oxide layer to explain the importance of the fact that the neutral region resistance value is considered in calculating the interface state density distribution from the nonideal forward bias current–voltage (I–V) characteristics. The diodes with the native oxide layer (metal–insulating layer–semiconductor (MIS)) showed nonideal I–V behavior with an ideality factor value of 1.310 and the barrier height value of 0.746eV. An ideality factor value of 1.065 and a barrier height value of 0.743eV were obtained for the diodes without the native oxide layer (MS). At the same energy position near the top of the valance band, the calculated interface states density (Nss) values, obtained without taking into account the series resistance of the devices (i.e. without subtracting the voltage drop across the series resistance from the applied voltage values V) is almost one order of magnitude larger than Nss values obtained by taking into account the series resistance.

The effects of the time-dependent on the characteristic parameters of polypyrrole/ p-type Si/Al diode

A detailed study of the effects of the time-dependent or aging on the characteristic parameters of polypyrrole/ p-type Si/Al structure has been presented. The polypyrrole film has been formed on a p-type Si substrate by means of an anodization process. The polypyrrole/ p-Si contact has demonstrated clearly rectifying behavior by the current–voltage curves studied at room temperature. The current–voltage ( I– V) curves of the diode have been measured immediately, 7, 15, 30, 60 and 90 days after fabrication of the polypyrrole/ p-Si contact. It has been seen that the characteristics parameters such as barrier height, ideality factor and series resistance of polypyrrole/ p-type Si/Al structure have changed with increasing ageing time. Furthermore, the density distribution of interface states of the device was obtained from the forward bias I– V characteristics. The fact that the diode shows non-ideal I– V behavior with increasing ageing time may be ascribed to a slow replacement of the initial doping agent by oxygen and this process certainly plays a role in the aging of the diode.

Study of the effect of interface state charges on field-effect mobility of n-channel 6H-SiC MOSFET

The effect of interface state charges on the field-effect mobility of n-channel 6H-SiC MOSFET is analyzed based on the nonuniform distribution of interface state density in the energy gap. The results of the analysis show that interface state charges have the influence of lowering the field-effect mobility in n-channel SiC MOSFET. A relationship has been established between the ratio of the experimentally determined field-effect mobility to the inversion-layer carrier mobility and interface states.

Determination of the density distribution of interface states from high- and low-frequency capacitance characteristics of the tin/organic pyronine-B/p-type silicon structure.

Determination of the density distribution of interface states from high- and low-frequency capacitance characteristics of the tin/organic pyronine-B/p-type silicon structure.

Shallow states at SiO2/4H-SiC interface on (112̄0) and (0001) faces

Shallow interface states at SiO2/4H-SiC were examined on (112̄0) and (0001) faces using metal–oxide–semiconductor (MOS) capacitors. The MOS capacitors were fabricated by wet oxidation on both faces to investigate the difference in the energy distribution of interface state density. The parallel conductance as a function of frequency was measured at room temperature, and high-frequency capacitance (C)–voltage (V) curves were measured both at room temperature and 100 K. By the conductance method, the interface state density on (112̄0) was revealed smaller than on (0001) at shallow energies, while at deeper energies the relation changes to opposite situation. High-frequency C–V curves at 100 K show a large positive flatband voltage shift and a large injection-type hysteresis on (0001) samples, while those were small on (112̄0), indicating another evidence of smaller interface state density near the conduction band edge on (112̄0).

Optimization and Interface Characterization of a Novel Oxide-Free Insulated Gate Structure for InP Having an Ultrathin Silicon Interface Control Layer

Attempts were made to characterize and optimize the novel oxide-free insulated gate structure for InP, having an ultrathin Si interface control layer (Si ICL). An in situ X-ray photoelectron spectroscopy (XPS) study indicated that P deficiency took place on the InP surface by the irradiation of a high-energy Si beam during the MBE growth of Si ICL. Based on this, a modified gate structure having an In0.53Ga0.47As cap layer on the InP surface for prevention of phosphorus loss was proposed and its interface properties were investigated. A careful design for quantum state control indicated that the Si ICL thickness should be reduced down to 0.5 nm for the InGaAs cap thickness of 3 nm. In situ XPS spectra showed that no pronounced desorption of As or P took place from the surface in the new gate structure. In situ contactless C–V measurement showed a low and wide interface state density distribution with a minimum of 2×1011 cm-2 eV-1. An InP MISFET test device with a gate length of 2 µm exhibited a maximum gm of 123 mS/mm and a high drain current of 389 mA/mm. These results indicated the effectiveness of the novel oxide-free insulated gate structure for application to InP power MISFETs as well as to surface passivation.

Gated photoluminescence study of oxide-free InP MIS structure having an ultrathin silicon interface control layer

In order to investigate the effectiveness of a novel oxide-free surface passivation approach for InP, using an ultrathin silicon interface control layer (Si ICL), gated photoluminescence characteristics of the Si 3N 4/Si ICL/n-InP metal–semiconductor–insulator (MIS) structure were studied at room temperature. As compared with gated PL spectra of Si 3N 4/n-InP MIS without Si ICL, PL intensities of the sample with Si ICL were much more strongly modulated by the gate voltage. The interface state density distribution was estimated by an optical analog of the Terman’s C– V analysis and a good agreement with the C– V analysis was obtained. The result indicates complete removal of Fermi level pinning over the entire bandgap in the novel oxide-free MIS structure.

Atomic-scale processes involved in long-term changes in the density of states distribution at the Si/SiO2 interface

We utilize very sensitive magnetic resonance measurements to observe changes in the densities of interface trap centers hundreds of hours after irradiation. Our observations provide direct atomic-scale evidence for slow changes in Si/SiO2 interface-state density distributions which appear after the devices have been damaged. Our observations also explain (at least in part) why different groups report somewhat different shapes for the density of interface states in the silicon band gap.

The effect of series resistance on calculation of the interface state density distribution in Schottky diodes

This work presents an attempt related to the importance of the fact that the series resistance value is considered in calculating the inter-face state density distribution from the non-ideal forward bias current–voltage (I-V) characteristics of Au/n-Si Schottky barrier diodes (SBDs). To examine the consistency of this approach, Au/n-Si SBDs with Si bulk thicknesses of 200 and 400μm have been prepared. Both diodes showed non-ideal I-V behaviour with ideality factors of 1.14 and 1.12, respectively, and thus it has been thought that the diodes have a metal–interface layer–semiconductor configuration. At the same energy position near the bottom of the conduction band, the interface state density (N SS) values, without taking into account the series resistance value of the devices, are almost one order of magnitude larger than the N SS values obtained taking into account the series resistance value.

Structural studies of 20 keV oxygen-implanted silicon

Silicon wafers were implanted with 20 keV O 2 + up to total fluence of 1×10 18 O 2 + cm −2 to synthesize SiO 2 layers. The FTIR, ESR and C– V studies of as-implanted samples and samples nitrogen-annealed at 500°C and 800°C are reported. The FTIR spectrum of the as-implanted sample shows absorption bands corresponding to the stretching (1050 cm −1, strong), the bending (800 cm −1, weak) and the rocking (415 cm −1, weak) modes of SiO 2. The peaks shift towards higher wave number on annealing. The ESR signal of the as-implanted sample exhibits an isotropic g-value 2.0028, the line width 3.75 G and the spin density 1.1×10 16 cm −2 which disappears on annealing at 800°C. The interface state density distribution as a U-shape and a minimum value of ∼ 7–8×10 11 cm −2 eV −1 .

Effect of thermal annealing on Co/n-LEC GaAs (Te) Schottky contacts

The Co/n-GaAs(Te) Schottky barrier diodes have been annealed at temperatures from 100 to 300°C for 5 min and from 350 to 800°C for 1 min in N 2 atmosphere. Some expressions have been obtained to interpret the relation between the experiment barrier height Φ b,o and equilibrium interface charge density Q ss(0) depending on annealing temperature. The Φ b,o value has increased and Q ss(0) is decreased with increasing annealing temperature up to 550°C. This increase in the barrier height has been attributed to the value of positive Q ss(0), which is responsible for the Fermi level pinning. The relation between the Φ b,o and Q ss(0) depending on annealing temperature is in very good agreement with that of the interface state density distribution especially in the mid-gap.

Potential barrier formed at n-ZnSe regrowth homointerface by molecular beam epitaxy

Electrical properties of n-ZnSe homointerfaces formed by MBE regrowth process have been investigated by I– V and C– V measurements of Au/n-ZnSe Schottky diodes, and their analyses considering the interface state density distribution. I– V and C– V behavior of an air-exposed regrown sample was simultaneously fitted by using a superposed distribution of a U-shape and a discrete distribution of interface states with their density between 10 12 and 10 13 cm −2 eV −1. Such a high-density of interface states was somewhat decreased by regrowth pretreatments using an HCl solution and saturated bromine water.

Measurement of Energetic and Lateral Distribution of Interface State Density in Fully-Depleted Silicon on Insulator Metal-Oxide-Semiconductor Field-Effect Transistors

A new modification of the charge pumping (CP) technique based on the effect of reverse pulse bias on suppression of the geometric component is proposed in order to accurately determine the energetic and lateral distribution of interface state density (Dit) in fully-depleted silicon on insulator metal-oxide-semiconductor field-effect transistors (FD SOI MOSFETs). A comparison of the conventional CP techniques with the proposed method is also presented. It is demonstrated that using the proposed method, the precise estimation of the energetic and lateral distribution of Dit can be simply obtained without interference from the geometry-dependent effect which often leads to the great difficulties in data interpretation in the conventional CP methods.

Interface state density in n-MOSFETs with Si-implanted gate oxide measured by subthreshold slope analysis

The effects of B +-channel implantation before gate oxidation and heavy Si implantation into the gate oxide on the interface state density distribution D it in the energy gap of n-MOSFETs are analyzed by a subthreshold slope ( S) method. For MOSFETs without Si-implantation, the measured D it distributions are independent of the B +-dose and are similar to those in the literature. For the Si-implanted MOSFETs, reasonable D it distributions dependent on the Si-implantation condition are obtained by assuming the same surface potential Ψ S at each threshold voltage as for MOSFETs without Si implantation. For all MOSFETs measured the estimated D it near mid-gap has about twice the value obtained from the C– V method. The subthreshold slope method is not universally applicable due to the problems of accurate determination of the substrate carrier concentration resulting in a Ψ S error and complete rejection of depletion capacitance, especially for high-dose Si-implanted MOSFETs.