Estimation for the capture cross-sections of surface state on p-Si surface by photovoltaic method

A new method which can nondestructively measure the surface-state density (SSD) D_s and estimate the capture cross-sections (CCS) of surface state σ⁰_n and σ⁻_p on surface of p-type semiconductor crystals is proposed. This method is based on the photovoltage measurements at various temperatures. The photovoltage experiment was carried out with a (1 1 1) p-type Si single crystal (N_A=4.8×10¹⁴ cm ⁻³). Owing to that the surface barrier height φ_BP=0.6421 V and the surface-recombination velocity s_n=9.6×10³ cm s⁻¹ of this sample can be determined, the SSD D_s=1.2×10¹¹ cm⁻² eV⁻¹ can therefore be obtained, furthermore CCS σ⁰_n≈5×10⁻¹⁴ cm² and σ⁻_p≈2×10⁻¹⁰ cm² can also be estimated. These results are consistent with that of related reports obtained by other methods.     

CoSi2 ohmic contacts to n-type 6H---SiC

Cobalt disilicide (CoSi₂) ohmic contacts possessing low specific contact resistivity (_c < 3.0 ± 0.4 × 10⁻⁵ ωcm²) to n-type 6H---SiC are reported. The contacts were fabricated via sequential electron-beam evaporation of Co and Si layers followed by a two-step vacuum anealing process at 500 and 900°C. Stochiometry of the contact so formed was confirmed by Rutherford backscattering spectrometry and X-ray diffraction. Specific contact resistivities were obtained via current-voltage (I-V) analysis at temperatures ranging from 25 to 500°C. _c is compared as a function of carrier concentration, current density, temperature and time at elevated temperature.     

Pt-based metallization of PMOS devices for a compatible monolithic integration of semiconducting/Yba2Cu3O7−δ superconducting devices on silicon

Mo, Pt, Pt/Mo and Pt/Ti thin films have been deposited onto Si and SiO₂ substrates by RF sputtering and annealed in the YBa₂Cu₃O_7−δ (YBCO) growth conditions. The effect of annealing on the sheet resistance of unpatterned layers was measured. A Pt-based multilayered metallization for the PMOS devices was proposed and tested for a compatible monolithic integration of semiconducting devices and YBCO sensors on the same silicon substrate. The best results were obtained with a Pt/Ti/Mo-silicide structure showing 0.472 Ω_□ interconnect sheet resistivity and 2×10⁻⁴ Ω cm² specific contact resistivity after annealing for 60 min at 700 °C in 0.5 mbar O₂ pressure.     

Stability of hydrogen in ScAlMgO4

Hydrogen as ²H was incorporated into ScAlMgO₄ by both ion implantation and by exposure to a plasma at 250°C. In the implanted material diffusion begins at 500°C and most of the hydrogen is lost by ≤ 750°C. This thermal stability for hydrogen retention is considerably lower than for other substrate materials for GaN epilayer growth, such as Al₂O₃ and SiC. There is minimal permeation of ²H from a plasma at 250°C (D_H ≤ 5 × 10⁻¹⁶ cm² s⁻¹) in ScAlMgO₄, and thus unintentional hydrogen incorporation into GaN overlayers should be minimal at typical growth temperatures.     

Electrical characteristics of GaAsP Schottky barrier diodes

Schottky barrier diodes of chromium on n-type epitaxial gallium arsenide phosphide (GaAsP) were studied from 25°C to 440°C. The diodes showed significant rectification properties up to a temperature of 440°C. At high temperature the reverse leakage current was 1.15 mA at 25 V with a diode area of 1.14×10⁻³ cm² as compared with 0.25-μA current at room temperature. The n factor derived from the slope of the ln I vs. V curves was 1.1. The barrier height for chromium was found to be 1.25 eV from the capacitance measurements and 1.12 eV from the saturation current vs. temperature measurements. The slope of the C-V curves yielded a carrier concentration of 6.0×10¹⁵ carriers per cm³.     

Carrier recombination in single crystal PbSe

The photoconductivity decay curves after illumination of single crystal n- and p-type PbSe were analysed assuming recombination through different localized impurity levels in conjunction with direct recombination. The lifetimes deduced for direct (Auger and radiative) recombination below 250 K were in agreement with the calculated values for carrier concentrations 2·10¹⁷ cm⁻³. Furthermore, the existence of up to three impurity levels was concluded from the longer lifetime-components present in the decay curves. Appropriate approximations of the general recombination theory yielded energies separated between 20 and 50 meV from the nearer band edge and minority carrier cross sections 10⁻¹⁷−4·10⁻¹⁹ cm² in the temperature range 250-100 K, and majority carrier cross sections 10⁻¹⁹−10⁻²⁰ cm² at T < 100 K for these levels.     

GaN p–n junction diode formed by Si ion implantation into p-GaN

²⁸Si⁺ implantation into Mg-doped GaN, followed by thermal annealing in N₂ was performed to achieve n⁺-GaN layers. The carrier concentrations of the films changed from 3×10¹⁷ (p-type) to 5×10¹⁹ cm⁻³ (n-type) when the Si-implanted p-type GaN was properly annealed. Specific contact resistance (ρ_c) of Ti/Al/Pt/Au Ohmic contact to n-GaN, formed by ²⁸Si⁺ implantation into p-type GaN, was also evaluated by transmission line model. It was found that we could achieve a ρ_c value as low as 1.5×10⁻⁶ Ω cm² when the metal contact was alloyed in N₂ ambience at 600 °C. Si-implanted GaN p–n junction light-emitting diodes were also fabricated. Electroluminescence measurements showed that two emission peaks at around 385 and 420 nm were observed, which could be attributed to the near band-edge transition and donor-to-acceptor transition, respectively.     

Schottky barrier height of a new ohmic contact NiSi2 to n-type 6H-SiC

We present a new ohmic contact material NiSi₂ to n-type 6H-SiC with a low specific contact resistance. NiSi₂ films are prepared by annealing the Ni and Si films separately deposited on (0 0 0 1)-oriented 6H-SiC substrates with carrier concentrations (n) ranging from 5.8×10¹⁶ to 2.5×10¹⁹ cm⁻³. The deposited films are annealed at 900 °C for 10 min in a flow of Ar gas containing 5 vol.% H₂ gas. The specific contact resistance of NiSi₂ contact exponentially decreases with increasing carrier concentrations of substrates. NiSi₂ contacts formed on the substrates with n=2.5×10¹⁹ cm⁻³ show a relatively low specific contact resistance with 3.6×10⁻⁶ Ω cm². Schottky barrier height of NiSi₂ to n-type 6H-SiC is estimated to be 0.40±0.02 eV using a theoretical relationship for the carrier concentration dependence of the specific contact resistance.     

High temperature ohmic contacts to 3C–silicon carbide films

Currently, large-area 3C–SiC films are available from a number of sources and it is imperative that stable high temperature contacts be developed for high power devices on these films. By comparing the existing data in the literature, we demonstrate that the contact behavior on each of the different polytypes of SiC will vary significantly. In particular, we demonstrate this for 6H–SiC and 3C–SiC. The interface slope parameter, S, which is a measure of the Fermi-level pinning in each system varies between 0.4–0.5 on 6H–SiC, while it is 0.6 on 3C–SiC. This implies that the barrier heights of contacts to 3C–SiC will vary more significantly with the choice of metal than for 6H–SiC. Aluminum, nickel and tungsten were deposited on 3C–SiC films and their specific contact resistance measured using the circular TLM method. High temperature measurements (up to 400°C) were performed to determine the behavior of these contacts at operational temperatures. Aluminum was used primarily as a baseline for comparison since it melts at 660°C and cannot be used for very high temperature contacts. The specific contact resistance (ρ_c) for nickel at room temperature was 5×10⁻⁴ Ω cm², but increased with temperature to a value of 1.5×10⁻³ Ω cm² at 400°C. Tungsten had a higher room temperature ρ_c of 2×10⁻³ Ω cm², which remained relatively constant with increasing temperature up to 400°C. This is related to the fact that there is hardly any reaction between tungsten and silicon carbide even up to 900°C, whereas nickel almost completely reacts with SiC by that temperature. Contact resistance measurements were also performed on samples that were annealed at 500°C.     

Silicon nano-particles in SiO2 sol–gel film for nano-crystal memory device applications

A novel 2-bit nano-silicon based non-volatile memory is proposed to double memory density. The thin film structure exhibits two conduction states (ON and OFF) at different voltages and has a cost-effective structure. The structure utilizes the good electrical properties of fluorinated SiO₂ thin films, together with the bi-stable properties conferred by the nano-silicon particles therein embedded. A polymeric layer of 8-hydroxyquinoline aluminum salt (Alq3) further deposited on the top of the nano-particle layer through chemical evaporation and a silver paste contact determines the final structure. The positive 0–15 V scan reveals two discontinuities with an ON/OFF ratio of 10⁴–10⁵ (2–4 V) and OFF/ON of 10³ (12.5–13.0 V). The reverse scan displays again two distinct thresholds, range of 10.5–11.0 V (ON/OFF ratio 10⁻³), respectively, 0.5 V (OFF/ON ratio 10⁻⁵–10⁻⁴).     

The intervalley X6→Γ6, L6 scattering time in GaAs measured by ultrafast pump-probe infrared absorption spectroscopy

A direct measurement of the dynamics of electrons in the X₆ valley for a GaAs crystal by time-resolved absorption spectroscopy is reported for the first time. IR picosecond probe pulses were used to monitor the growth and decay of the population in the X₆ valley subsequent to excitation by a 527 nm pump pulse. The intervalley X₆→Γ₆, L₆ scattering time t_x of 0.70 ± 0.50 ps is determined and the crossection for the X₆→X₇ transition is estimated to be 1.8 × 10⁻¹⁶ cm².     

Injection electroluminescence in metal-semiconductor tunnel diodes

Injection electroluminescence has been studied in metal-semiconductor (MS) and in metal-insulator-semiconductor (MIS) tunnel diodes. The diodes were fabricated from degenerately doped p-type ZnTe. Bandgap recombination radiation has been observed at 293°K, 77°K and 4°K. The linewidth narrows from approximately 120 Å at 293°K to approximately 60 Å at temperatures below 77°K. External efficiencies of 10⁻⁴ to 10⁻⁶ have been observed. For current densities below 10³ A/cm² the light output increases as the fourth or fifth power of the current density. For current densities greater than 10³ A/cm² the light varies linearly or slightly sublinearly with current density. A new model for the emission from MS tunnel diodes is proposed which accounts for the observation that light emission occurs when the semiconductor is negatively biased. No evidence of stimulated emission has been observed up to current densities of 10⁴ A/cm².     

Trap density of silicon chlorine oxides

By measuring the ramp voltage I–V characteristics, we obtained the oxide trap density and capture cross-section for (O₂ + HCl) dry oxidized samples in the temperature range 900–1100°C. It was found that the oxide trap density increases with an increase in the oxidation temperature. The activation energy of oxide trap incorporation is of the order of 4 eV. The capture cross-section determined for the oxide traps is of the order of 10⁻¹⁴ cm².     

Reliability of ultra thin ZrO2 films on strained-Si

Ultra thin high-k zirconium oxide (equivalent oxide thickness 1.57 nm) films have been deposited on strained-Si/relaxed-Si_0.8Ge_0.2 heterolayers using zirconium tetra-tert-butoxide (ZTB) as an organometallic source at low temperature (<200 °C) by plasma enhanced chemical vapour deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. The trapping/detrapping behavior of charge carriers in ultra thin ZrO₂ gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Stress induced leakage current (SILC) through ZrO₂ is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of ZrO₂ layer. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of 10⁻¹⁹ cm² as compared to 10⁻¹⁶ cm² in SiO₂ has been observed. The trapping charge density, Q_ot and charge centroid, X_t are also empirically modeled. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating layer. Dielectric breakdown and reliability of the dielectric films have been studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t_bd > 1500 s) is observed under high constant voltage stress.     

On the behaviour of buried oxygen implanted layers in highly doped GaAs

Highly doped GaAs substrate material (doping level 10¹⁸ cm⁻³) has been implanted with 350 keV O⁺ ions with doses of 10¹⁴ – 10¹⁶ cm⁻² to produce high resistivity layers which are stable at high temperatures. LPE growth of flat GaAs epilayers onto the implanted wafers was achieved up to doses of about 1 × 10¹⁵ O⁺/cm² and 5 × 10¹⁵O⁺/cm² for RT and 200°C implants, respectively. N-o-n and p-o-n structures (o: oxygen implanted) were fabricated in which breakdown voltages of up to 15 V were obtained. Examples for application of this isolation technique are shown.     

Electrical characteristics of B-implanted p-channelMNOS transistors

Boron ions (¹¹B⁺ of 3·7 to 7·4 × 10¹¹/cm² were implanted at 60–120 keV into the channel region of p-channel MNOS double layer insulated gate field effect transistors through 920–940 Å of SiO₂ and various thicknesses (300–1800 Å) of Si₃N₄ deposited on SiO₂. Subsequent annealing was performed in a nitrogen atmosphere at 1000°C for 30 min. Acceleration energy, implant dose and Si₃N₄ thickness dependences of the shift of the threshold voltage showed good agreement with the calculated results based on Ishiwara and Furukawa's theory for distribution of implanted atoms in the double layered substrate, using the projected ranges and standard deviations larger than LSS predictions by the factor of 1·2 for SiO₂ and 1·3 for Si₃N₄, respectively. The results on the gain terms and the breakdown voltages were qualitatively the same as those of ¹¹B⁺-implanted p-channel MOS transistors.     

High current bulk GaN Schottky rectifiers

GaN Schottky rectifiers employing guard-ring and SiO₂ edge termination show almost ideal forward current characteristics, with ideality factor 1.08 and specific on-state resistance as low as 2.6×10⁻³ Ω cm². A maximum forward current of 1.72 A at 6.28 V was achieved under pulsed (10% duty cycle) conditions. The reverse breakdown voltage was inversely dependent on rectifier area. The presence of defects in the GaN still dominates the reverse leakage, with both field emission and thermionic field emission contributions present. The parallel-plane breakdown voltage is never reached, even with the use of multiple edge termination methods, but the results show the promise of GaN rectifiers for power conditioning and electric utility applications.     

An investigation of LixNi1−x,O as a mixed-valence thermoelectric material

The mixed valence material, Li_xNi_1−xO, has been investigated as a potential thermoelectric material. Measurements of the Seebeck coefficient, (μ V/°C), electrical resistivity, ρ(Ω-cm), and thermal conductivity, k(W/cm°C) have been made as a function of temperature and lithium concentration. The thermoelectric figure of merit, Z(²/ρk), reaches a value of approximately 1·4×10⁻⁴ at 1100°C for the composition Li_0.04Ni_0.96O.     

Direct recombination in GaAs and some consequences in transistor design

Experiments are presented indicating that the recombination rate R in GaAs is given by the expression R = Bpn. The theory of Hall for direct transition is used to calculate the value of B as 1·4×10⁻¹⁰ cm³/sec. Practical GaAs transistors are shown to be feasible if base widths of 1 μ are used.     

Analysis of I–V measurements on PtSi-Si Schottky structures in a wide temperature range

I–V Measurements on PtSi-Si Schottky structures in a wide temperature range from 90 to 350 K were carried out. The contributions of thermionic-emission current and various other current-transport mechanisms were assumed when evaluating the Schottky barrier height Φ₀. Thus the generation-recombination, tunneling and leak currents caused by inhomogeneities and defects at the metal-semiconductor interface were taken into account.

Taking the above-mentioned mechanisms and their temperature dependence into consideration in the Schottky diode model, an outstanding agreement between theory and experiment was achieved in a wide temperature range.

Excluding the secondary current-transport mechanisms from the total current, a more exact value of the thermionic-emission saturation current I_te and thus a more accurate value ofΦ_b was reached.

The barrier height Φ_b and the modified Richardson constant A^** were calculated from the plot of thermionic-emission saturation current I_te as a function of temperature too. The proposed method of finding Φ_b is independent of the exact values of the metal-semiconductor contact area A and of the modified Richardson constant A^**. This fact can be used for determination of Φ_b in new Schottky structures based on multicomponent semiconductor materials.

Using the experimentally evaluated value A^** = 1.796 × 10⁶ Am⁻²K⁻² for the barrier height determination from I–V characteristics the value of Φ_b = 0.881 ± 0.002 eV was reached independent of temperature.

The more exact value of barrier height Φ_b is a relevant input parameter for Schottky diode computer-aided modeling and simulation, which provided a closer correlation between the experimental and theoretical characteristics.