Interface state density in Au-nGaAs Schottky diodes

A method for determining the surface state density in Schottky diodes taking into account both I–V and C–V data while considering the presence of a deep donor level is presented. The model assumes that the barrier height is controlled by the energy distribution of surface states in equilibrium with the metal and the applied potential and does not include, explicitly, an interfacial layer. The model was applied to extract interface state densities of Au-nGaAs guarded Schottky diodes fabricated from bulk and VPE (100) GaAs with carrier conentrations between 3 × 10¹⁵ and 8 × 10¹⁶ cm^?3. These diodes exhibited ideality (n) factors of approximately 1.02 and room temperature saturation current densities ～10^?8 A/cm². This model is in substantial agreement with forward bias measurements over the 77–360°K temperature range investigated, in that a temperature-independent energy distribution of interface states was obtained. In reverse bias the interface state model is most valid with the higher carrier concentration material and at high temperature and low bias voltage. Typical interface state densities from 0.07 eV above the zero bias Fermi level to 0.01 eV below the Fermi level were 2 × 10¹³ cm^?2 eV^?1. The validity of the model under reverse bias is restricted by a non-thermionic reverse current, thought to be enhance field emission from traps.     

Influence of Annealing on Electrical Properties of an Organic Thin Layer-Based n-Type InP Schottky Barrier Diode

The electrical properties of a fabricated Au/polymethylmethacrylate (PMMA)/n-InP Schottky barrier diode have been analyzed for different annealing temperatures using current–voltage (I–V) and capacitance–voltage (C–V) techniques. It is observed that the Au/PMMA/n-InP structure shows excellent rectifying behavior. The extracted barrier height and ideality factor of the as-deposited Au/PMMA/n-InP Schottky contact are 0.68 eV (J–V)/0.82 eV (C–V) and 1.57, respectively. However, the barrier height (BH) of the Au/PMMA/n-InP Schottky contact increases to 0.78 eV (J–V)/0.99 eV (C–V) when the contact is annealed at 150°C for 1 min in nitrogen atmosphere. Upon annealing at 200°C, the BH value decreases to 0.72 eV (J–V)/0.90 eV (C–V) and the ideality factor increases to 1.48. The PMMA layer increases the effective barrier height of the structure by creating a physical barrier between the Au metal and the n-InP. Cheung’s functions are also used to calculate the series resistance of the Au/PMMA/n-InP structure. The interface state density (N _ss) is found to be 6.380 × 10¹² cm^?2 eV^?1 and 1.916 × 10¹² cm^?2 eV^?1 for the as-deposited and 150°C-annealed Au/PMMA/n-InP Schottky contacts, respectively. These results indicate that the interface state density and series resistance have a significant effect on the electrical characteristics of Au/PMMA/n-InP Schottky barrier devices. Finally, it is noted that the diode parameters change with increasing annealing temperature.     

Theory and experiment for silicon Schottky barrier diodes at high current density

Metal-silicon Schottky barrier diodes exhibit n values which theoretically vary as a function of doping and applied voltage. The expected variation depends on which theoretical model is used to describe the current transport.Titanium n-type silicon barriers were prepared. At a doping level of 3 × 10¹⁵ cm^?3 the barrier height and n-value measured at 100 mV were 0.485±0.005 V and 1.02±0.01 whereas for a doping level of 2 × 10¹⁴ cm^?3 the corresponding values were 0.500±0.005 V and 1.18±0.05.The experimental variation of the diode n value as a function of semiconductor band bending showed good agreement with the thermionic-diffusion model of Crowell and Beguwala: n values increased rapidly as the band bending β → 2, and n values were highest at a given β for diodes with the lowest doping concentration. Similar results were obtained by measurements on magnesium and aluminium barriers on n-type silicon.An analysis of the results has shown that the variation of the diode saturation current I_s follows the predictions of the thermionic-diffusion theory, although there were some anomalies at high current densities. The anomalies did not result from variation of the width of the undepleted region of the epitaxial silicon layer or from diode self-heating effects.     

Hafnium-ntype silicon Schottky barriers

This paper describes the electrical properties of hafnium-/n-type/silicon contacts. These contacts were found to be Schottky barriers with a low barrier height. Polished and chemically cleaned 〈111〉 silicon wafers with a donor concentration N_d = 7 × 10²² m^?3 were used to fabricate experimental Schottky barrier structures. For the Schottky barrier height φ_bn and the ideality factor n values were found of 0.47 V and 1.07–1.11, respectively. It is concluded that due to their low forward voltage drop and good rectifying properties, Hf-nSi contacts can be applied in microwave Schottky barrier diodes.     

Theoretical analysis of a novel MPN gallium arsenide Schottky barrier solar cell

Theoretical analysis for a novel Au-p-n GaAs Schottky barrier solar cell has been made in this note. It is shown that barrier height equal to the energy band gap of GaAs can be obtained in the proposed cell structure if the thickness and dopant density of the p-GaAs layer are properly chosen. Calculations of the barrier height as function of the thickness and dopant density of the p-layer have been carried out for a Au-p-n GaAs Schottky barrier cell. It is shown that AMO efficiency around 22% can be achieved in the proposed solar cell when N_D = 10¹⁶ cm^?3, N_A = 8 × 10¹⁸ cm^?3 and $\text{W}{}_{\mathrm{p}}\text{= 100}\text{A}\text{?}$ are chosen.     

Observation of electron traps in electrochemically deposited CdTe films

The I–V and C-V data of Schottky devices formed on electrodeposited n-CdTe films are interpreted to determine the principle trap energy and density. The observed trap is an electron trap located at 0.55 eV below the conduction band with a density of ～7 × 10¹⁵/cm³. This correlates well with the values reported for CdTe prepared by different methods. Nickel is found to be an injecting contact to electrodeposited CdTe films. Au/n-CdTe barrier height is determined to be 0.75–0.85 eV for Schottky devices.     

The interface between Hg1−xCdxTe and its native oxide

The results of a study of the electrical properties of the interface between Hg_1?xCd_xTe with x = 0.21 and its native oxide at 77°K are presented. The native oxide is formed by anodic oxidation and results in an interface with reproducible properties. The surface charge, the surface mobility and the effective lifetime are obtained from galvanomagnetic measurements and are related to the semiconductor bulk parameters, the oxide thickness and the annealing conditions. The surface state charge and the metal-semiconductors work function difference are obtained from the shift of the flat band voltage of metal-oxide-semiconductor (MOS) capacitor characteristics. The interface between Hg_1?xCd_xTe and its native anodic oxide is characterized by a density of fast surface states of the order of 5 × 10¹¹cm^?2 (eV^?1) near the middle of the bandgap. The density of states increases towards the band edges to the order of 10¹³cm^?2 (eV^?1). The measured flat band voltage is approximately ?0.5 V for an oxide thickness of 500 Å and for an n-type semiconductor with an electron carrier concentration in the range 1–3 × 10¹⁵cm^?3 at 77°K. The fixed oxide surface state charge is positive for both p-type and n-type semiconductors and is of the order of 6 × 10¹¹ charges per cm^?2. The surface properties, the significance and the reproducibility of the results are evaluated.     

Current diffusion effects in titanium-N silicon schottky diodes

Measurements of the reverse current-voltage characteristics of titanium-n silicon Schottky barrier diodes are presented which demonstrate that diffusion limited currents can occur in these diodes when the internal electric field is low. For the titanium-n silicon diodes, the low barrier height of 0.51 eV and doping concentration of 10¹⁵ cm^?3 result in an electric field of 8 × 10³ V cm^?1 at zero bias. An observed decrease in the reverse saturation current at low bias, previously described as anomalous, is now reconciled with the thermionic-diffusion theory of current flow, whoch predicts a reduction in A⁷, the effective Richardson constant, at internal fields below 10⁵ V cm^?1.     

Specific resistivity of a metal-n GaAs OHMIC contact with an intermediate N+ layer

The specific contact resistivity ρ_c of a metal-n GaAs structure, over a wide range of carrier concentrations in the intermediate layer (5 × 10¹⁸–5 × 10²⁰ cm^?3) and in the substrate (10¹⁵?10¹⁷ cm^?3) is calculated. The results which are presented graphically demonstrate the dependence of ρ_c on metal-semiconductor barrier height from 0.2 eV–0.8 eV. A comparison with the measured data of an alloyed AuGeNi-n GaAs system, suggests that the calculations corresponding to a concentration of 5 × 10¹⁸ cm^?3 in the layer and barrier height of 0.4 eV give the best fit based on the experimental observations. It is hoped that the results can be used as a guideline in developing ohmic contacts of ultra low resistance values.     

Analysis of thermal emission processes of electrons from arrays of InAs quantum dots in the space charge region of GaAs matrix

We thoroughly analyze admittance spectroscopy data on the temperature dependence of the rate of electron emission from the ground state of InAs quantum dots in the space-charge layer of a Schottky barrier on an n-GaAs matrix. The experimental results are described using a one-dimensional model of thermally activated tunneling with the involvement of virtual states. The shape of the potential barrier to be overcome by emitted electrons is selected by introducing the effective concentration of shallow donors such that the electron binding energies in the quantum dots were similar to those determined from the measured capacitance-voltage characteristics of the investigated structures. The obtained electron-capture cross sections increase with the ground-state binding energy (quantum dot size). The capture cross-section values for InAs quantum dots with average lateral sizes of 9 and 20 nm lie in the ranges 1 × 10^?14?2 × 10^?13 and 4 × 10^?12?2 × 10^?11 cm².     

Current-voltage characteristics of electric contacts on p-type ZnSe

The current-voltage characteristics of electric contacts made of different materials on p-type ZnSe that form Schottky barriers from 0.3 to 1.2 eV are studied theoretically using the formula $$J = \frac{{A^* T}}{k}\int_0^\infty {T(E)[F(E) - F(E - eV)]dE,} $$ where T(E) is the energy-dependent quantum tunneling probability and F(E) is the Fermi distribution function. The contribution to the total current of both the thermionic emission and the tunneling are therefore included. The net doping concentrations under study range from 1.0×10¹⁷ cm^?3 to 1.0×10¹⁹ cm^?3. The reverse bias voltage across the barrier at a current density of 200 A/cm² is used to assess whether the barrier is reduced to an ohmic contact. A barrier of 0.3 eV is already an ohmic contact at doping concentration p=1.0×10¹⁷ cm^?3, while a barrier of 1.2 eV still behaves like a diode event at p=1.0×10¹⁹ cm^?3.     

A study of recombination centers related to As-Sb nanoclusters in low-temperature grown gallium arsenide

Electronic traps in “low-temperature” GaAs (LT-GaAs) grown at 150°C were studied. The As-Sb clusters appearing in this material after annealing were located in a plane that contained a single Sb monolayer formed during growth. The diameter of the clusters was as large as 20 nm. For the purpose of measurement, Au-n-GaAs Schottky barriers were used, in which, for certain bias voltages, the space charge region enclosed the narrow LT-GaAs layer containing the plane of clusters. The bias-voltage dependence of the structure capacitance indicates that the majority of the electrons in this layer are captured by traps, whose energy level lies ～0.5 eV below the bottom of the conduction band. The energy density of states at this energy is 10¹⁴ cm^?2 eV^?1, which sharply decreases towards the midgap. The existence of traps with activation energies of ～0.5 eV for the thermal emission of electrons is confirmed by deep-level transient spectroscopy. The magnitude of the electroncapture cross section determined by this method is in the range 5 × 10^?14?1 × 10^?12 cm². It is assumed that traps of this type are related to large As-Sb clusters.     

The ohmic contact formation mechanism of Au/Pt/Pd ohmic contact to p-ZnTe

The ohmic contact formation mechanism and the role of Pt layer of Au(500Å) Pt(500Å)/Pd(100Å) ohmic contact to p-ZnTe were investigated. The specific contact resistance of Au/Pt/Pd contact depended strongly on the annealing temperature. As the annealing temperature increased, the specific contact resistance decreased and reached a minimum value of 6×10^?6 Θcm² at 200°C. From the Hall measurement, the hole concentration increased with the annealing temperature and reached a maximum value of 2.3×10¹⁹ cm^?3 at 300°C. The Schottky barrier height decreased with the increase of annealing temperature and reached a minimum value of 0.34 eV at 200°C and it was due to the interfacial reaction of Pd and ZnTe. Therefore, the decrease of contact resistance was due to the increase of doping concentration as well as the decrease of Schottky barrier height by the interfacial reaction of Pd ZnTe. The specific contact resistances of Au Pd, Au/Pt/Pd and Au/Mo/Pd as a function of annealing time was investigated to clarify the role of Pt layer.     

Radiation resistance of transistor-and diode-type SiC detectors irradiated with 8-MeV protons

Nuclear-particle detectors based on SiC with a structure composed of an n⁺-type substrate, a p-type epitaxial layer, and a Schottky barrier are studied. Structures with a ～10-µm-thick 6H-SiC layer exhibit transistor properties, whereas those with a ～30-µm-thick 4H-SiC layer exhibit diode properties. It is established that a more than tenfold amplification of the signal is observed in the transistor-type structure. The amplification is retained after irradiation with 8-MeV protons with a dose of at least 5×10¹³ cm^?2; in this case, the resolution is ≤10%. Amplification of the signal was not observed in the structures of diode type. However, there were diode-type detectors with a resolution of ≈3%, which is acceptable for a number of applications, even after irradiation with the highest dose of 2×10¹⁴ cm^?2.     

The Improvement of Electrical Characteristics of Pt/Ti Ohmic Contacts to Ga-Doped ZnO by Homogenized KrF Pulsed Excimer Laser Treatment

We investigated the effect of KrF excimer laser surface treatment on Pt/Ti ohmic contacts to Ga-doped n-ZnO (N_d = 4.3 × 10¹⁷ cm^?3). The treatment of the n-ZnO surfaces by laser irradiation greatly improved the electrical characteristics of the metal contacts. The Pt/Ti ohmic layer on the laser-irradiated n-ZnO showed specific contact resistances of 2.5 × 10^?4 ～ 4.8 × 10^?4 Ω cm² depending on the laser energy density and gas ambient, which were about two orders of magnitude lower than that of the as-grown sample, 8.4 × 10^?2 Ω cm². X-ray photoelectron spectroscopy and photoluminescence measurements showed that the KrF excimer laser treatments increased the electron concentration near the surface region of the Ga-doped n-ZnO due to the preferential evaporation of oxygen atoms from the ZnO surface by the laser-induced dissociation of Zn-O bonds.     

Schottky barrier height modification in Au/n-type 6H-SiC structures by PbS interfacial layer

We have prepared the Au/PbS/n-6H-SiC Schottky diodes with interface layer and the reference Au/n-6H-SiC/Ni Schottky diodes without interface layer to realize Schottky barrier height (SBH) modification in the Au/SiC Schottky diodes. The BH reduction has been succeeded by the PbS interlayer to modify the effective BH by influencing the space charge region of the SiC. The PbS thin layer on the SiC was formed by the vacuum evaporation. The SBH values of 0.97 and 0.89 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. X-ray diffraction (XRD) study was carried out to determine the structural formation of the PbS on SiC. The reduction of the BH in the Au/PbS/n-6H-SiC Schottky diodes has been attributed to the fact that the interface states have a net positive interface charge in metal/n-type semiconductor contact, and thus the positive space charge Q_sc in the Au/PbS/n-6H-SiC Schottky diodes becomes smaller than if the interface state charges Q_ss were absent. The experimental carrier concentration value of 4.73 × 10¹⁷ cm⁻³ obtained from the forward and reverse bias capacitance-voltage characteristics for the Au/PbS/n-6H-SiC contacts is lower than the value of 5.52 × 10¹⁷ cm⁻³ obtained for the reference diode, and this is an evidence of the reduction of the BH by the modification of the space charge density of the SiC.     

A computer-aided simulation model for the I–V characteristic of M-n-p silicon Schottky-barrier diodes produced by use of low-energy arsenic-ion implantation

Current-transport properties of Al-n-p silicon Schottky-barrier diodes have been studied both experimentally and theoretically. An analytical model for the I-V characteristic of a metal-n-p Schottky barrier diode has been developed by using an interfacial layer-thermionic-diffusion model. Assuming a Gaussian distribution for the implanted profile, the barrier-height enhancement and ideality factor have been derived analytically. Using low energy (25 KeV) arsenic implantation with the dose ranged form 8 × 10¹⁰/cm² to 10¹²/cm², Al-n-p silicon Schottky barrier diodes have been fabricated and characterized. Comparisons between the experimental measurements and the results of computer simulations have been performed and satisfactory agreements between these comparisons have been obtained. The reverse I–V characteristics of the fabricated Al-n-p silicon Schottky barrier diodes can also be well simulated by the developed model.     

Deep levels in the band gap of GaN layers irradiated with protons

Deep-level transient spectroscopy was used to study the parameters of deep levels in the band gap of epitaxial n-GaN layers after irradiaton of the Schottky barriers with 1-MeV protons to a dose of 10¹² cm^?2. A deep level EP1 with an activation energy of 0.085 eV was introduced by irradiation into the upper half of the GaN band gap. The introduction rate of the corresponding defect was found to depend on the bias voltage applied to the Schottky barrier during irradiation.     

Tunneling Current in Oppositely Connected Schottky Diodes Formed by Contacts between Degenerate <Emphasis Type="Italic">n</Emphasis>-GaN and a Metal

The nonlinear behavior of the I–V characteristics of symmetric contacts between a metal and degenerate n-GaN, which form oppositely connected Schottky diodes, is investigated at free-carrier densities from 1.5 × 10¹⁹ to 2.0 × 10²⁰ cm^–3 in GaN. It is demonstrated that, at an electron density of 2.0 × 10²⁰ cm^–3, the conductivity between metal (chromium) and GaN is implemented via electron tunneling and the resistivity of the Cr–GaN contact is 0.05 Ω mm. A method for determining the parameters of potential barriers from the I–V characteristics of symmetric opposite contacts is developed. The effect of pronounced nonuniformity of the current density and voltage distributions over the contact area at low contact resistivity is taken into account. The potential-barrier height for Cr–n⁺-GaN contacts is found to be 0.47 ± 0.04 eV.     

Mechanism of dislocation-governed charge transport in schottky diodes based on gallium nitride

A mechanism of charge transport in Au-TiB _x -n-GaN Schottky diodes with a space charge region considerably exceeding the de Broglie wavelength in GaN is studied. Analysis of temperature dependences of current-voltage (I–V) characteristics of forward-biased Schottky barriers showed that, in the temperature range 80–380 K, the charge transport is performed by tunneling along dislocations intersecting the space charge region. Estimation of dislocation density ρ by the I–V characteristics, in accordance with a model of tunneling along the dislocation line, gives the value ρ ≈ 1.7 × 10⁷ cm^?2, which is close in magnitude to the dislocation density measured by X-ray diffractometry.