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.     

Electrical, structural, and optical characterization of free-standing GaN template grown by hydride vapor phase epitaxy

Electrical, structural, and optical properties of a free-standing 200 μm thick n-type GaN template grown by hydride vapor phase epitaxy have been investigated. Hall mobilities of 1100 and 6800 cm²/V s have been obtained at room temperature and 50 K, respectively. Quantitative analysis of acceptor concentration, donor concentration and donor activation energy has been conducted through simultaneous fitting of the temperature dependent Hall mobility and carrier concentration data which led to a donor concentration of 2.10×10¹⁶ cm⁻³ and an acceptor concentration of 4.9×10¹⁵ cm⁻³. The resultant donor activation energy is 18 meV. The analysis indicates that the dominant scattering mechanism at low temperatures is by ionized impurities. The extended defect concentrations on Ga- and N-faces were about 5×10⁵ cm⁻² for the former and about 1×10⁷ cm⁻² for the latter, as revealed by a chemical etch. The full width at half maximum of the symmetric (0 0 0 2) X-ray diffraction peak was 69″ and 160″ for the Ga- and N-faces, respectively. That for the asymmetric (10–14) peak was 103″ and 140″ for Ga- and N-faces, respectively. The donor bound exciton linewidth as measured on the Ga- and N-face (after a chemical etch to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.45 eV.     

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.     

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.     

Photoluminescence studies from micropillars fabricated on IV–VI multiple quantum-well semiconductor structure

Micropillars were fabricated on multiple quantum-well structure of PbSe/PbSrSe grown on top of BaF₂ substrate in molecular beam epitaxy (MBE). The photoluminescence spectra from the pillar structure, having a diameter of 5 μm and inter-pillar distance of 8 μm, was studied at various temperature starting from 77 to 300 K. There had been an approximately consistent red-shift of photoluminescence peak of 3.62 cm⁻¹ for unit K change in ambient temperature. The prominent and repeatable emission from the micropillars at various temperatures signified high crystalline nature of the fabricated micro-objects. This type of micropillar structure is one of the magnificent contenders of future opto-electronic micro-features.     

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.     

Interface characteristics of Ge3N4-(n-type) GaAs MIS devices

Passivation of GaAs surfaces was achieved by the deposition of Ge₃N₄ dielectric films at low temperatures. Electrical characteristics of MIS devices were measured to determine the interface parameters. From C-V-f and G-V-f measurements, density of interface states has been obtained as (4–6)×10¹¹ cm⁻² eV⁻¹ at the semiconductor mid-gap. Some inversion charge buildup was seen in the C-V plot although the strong inversion regime is absent. Thermally stimulated current measurements indicate a trap density of 5×10¹⁸−10¹⁹ cm⁻³ in the dielectric film, with their energy level at 0.59 eV.     

Intersubband lifetimes in Si/SiGe quantum wells

In the present work we report the first measurement of intersubband lifetimes in Si/Si_1−xGe_x quantum well samples. We have determined T₁ by a time resolved pump and probe experiment using the far infrared picosecond free electron laser source FELIX at Rijnhuizen, the Netherlands. In a sample with a well width of 50 Å and a sheet density of 2.1 × 10¹² cm⁻² we find a lifetime of 30 ps while 20 ps is observed for a density of 1.1 × 10¹² cm⁻² and a well width of 75 Å. We discuss acoustic phonon, as well as optical phonon intersubband scattering as possible limiting processes for the observed lifetimes in Si/SiGe and GaAs/AlGaAs quantum wells.     

Transport of the photoexcited electron-hole plasma in InP

Transport properties of the photoexcited electron-hole plasma in n-type InP have been studied by the spatial-imaged, time-resolved Raman scattering technique with 30μm and 0.1μm spatial resolution for lateral and perpendicular transport, respectively, and on a picosecond time scale. The plasma density ranging from 1 × 10¹⁶ to 2 × 10¹⁷ cm⁻³ was deduced from fitting of the Raman spectra with the plasmon-LO phonon scattering theory which took into account the contributions from free holes. In contrast to the experimental results of Young and Wan who found that ordinary diffusion equation was sufficient to fit their transient plasma density-time profiles in semi-insulating InP, our experimental measurements have shown that perpendicular transport (i.e., expansion into the bulk crystal) of the plasma in n-type InP can be very well described by a modified diffusion equation including the effect of drifting away from the surface based on a hydrodynamic model. The transient plasma density-time profiles were studied at T = 300K and for an initial injected plasma density n 2 × 10¹⁷ cm⁻³. The plasma has been found to expand laterally at a velocity V 5 × 10⁴ cm/sec and perpendicularly into the crystal at a velocity Vp 1.5 × 10⁵ cm/sec.     

Optoelectronic properties of Zn0.52Se0.48/Si Schottky diodes

Zn_0.52Se_0.48/Si Schottky diodes are fabricated by depositing zinc selenide (Zn_0.52Se_0.48) thin films onto Si(1 0 0) substrates by vacuum evaporation technique. Rutherford backscattering spectrometry (RBS) analysis shows that the deposited films are nearly stoichiometric in nature. X-ray diffractogram of the films reveals the preferential orientation of the films along (1 1 1) direction. Structural parameters such as crystallite size (D), dislocation density (δ), strain (ε), and the lattice parameter are calculated as 29.13 nm, 1.187 × 10⁻¹⁵ lin/m², 1.354 × 10⁻³ lin⁻² m⁻⁴ and 5.676 × 10⁻¹⁰ m respectively. From the I–V measurements on the Zn_0.52Se_0.48/p-Si Schottky diodes, ideality and diode rectification factors are evaluated, as 1.749 (305 K) and 1.04 × 10⁴ (305 K) respectively. The built-in potential, effective carrier concentration (N_A) and barrier height were also evaluated from C–V measurement, which are found to be 1.02 V, 5.907 × 10¹⁵ cm⁻³ and 1.359 eV respectively.     

Hydrogen “doped” thin film diamond field effect transistors for high power applications

Early predictions that diamond would be a suitable material for high performance, high power devices were not supported by the characteristics of diodes and field effect transistors (FETs) fabricated on boron doped (p-type) thin film material. In this paper commercially accessible polycrystalline thin film diamond has been turned p-type by the incorporation of near surface hydrogen; mobility values as high as 70 cm² V⁻¹ s⁻¹ have been measured for films with a carrier concentration of 5×10¹⁷ cm⁻³. Schottky diodes and metal–semiconductor FETs (MESFETs) have been fabricated using this approach which display unprecedented performance levels; diodes with a rectification ratio >10⁶, leakage currents <1 nA, no indication of reverse bias breakdown at 100 V and an ideality factor of 1.1 have been made. Simple MESFET structures that are capable of switching V_DS values of 100 V with low leakage and current saturation (pinch-off) characteristics have also been fabricated. Predictions based upon experiments performed on these devices suggest that optimised device structures will be capable of operation at power levels up to 20 W mm⁻¹, implying that thin film diamond may after all be an interesting material for power applications.     

Characteristics of polycrystalline films grown by ultrahigh vacuum chemical vapor deposition system

In situ boron-doped polycrystalline Si_1−xGe_x (poly-Si_1−xGe_x) films deposited by ultrahigh vacuum chemical vapor deposition (UHV/CVD) system were characterized. Optimum fitted values of grain boundary trap state densities, 4.0 × 10¹² cm⁻² and 4.9 × 10¹² cm⁻² were obtained for poly-Si and poly-Si_0.79Ge_0.21, respectively. The extracted average carrier concentration in the grain agrees with secondary ion mass spectroscopy (SIMS) analysis. In turn, we found that these films are suitable Hall elements to sense magnetic field. Experimental results show that the sensitivity decreased with the increasing input current, which can be well explained using the thermionic emission theory. Finally, we use these films to fabricate thin film transistors.     

The physics and fabrication of in situ back-gated (311)A hole gas heterojunctions

This paper reports the fabrication of an in situ back-gated hole gas on the (311)A surface of GaAs. The hole density can be varied from fully depleted to p_s = 2.1 × 10¹¹ cm⁻² with mobilities of up to μ = 1.1 × 10⁶ cm²V⁻¹ s⁻¹. It is seen that for carrier densities down to p_s = 4 × 10¹⁰ cm⁻² the mobility in the [ ] direction is greater than that in the [ ] direction. Using a combination of front- and back-gates we are able to keep the carrier density constant and deform the hole gas wavefunction such that the holes are pushed up against or moved further away from the heterointerface. Thus we are able to separately investigate the various scattering mechanisms that determine the mobility, and compare the experimental data with theoretical calculations based on the shape of the wavefunction.     

Process and device characterization of high voltage gallium arsenide P-i-N layers grown by an improved liquid phase epitaxy method

GaAs P-i-N layers with an i-region net doping of less than 10¹² cm⁻³ were grown on P⁺ and N⁺ substrates by a modified liquid phase epitaxy (LPE) method. Doping profiles and structural data obtained by varius characterization techniques are presented and discussed. A P⁺-P-i-N-N⁺ diode with a 25 μm-wide i-region exhibits a breakdown voltage of 1000 V, a t_rr of 50 ns, and reverse current densities (at V_R = 800 V) of − 3 × 10⁻⁶ A/cm² at 25°C and 10⁻² A/cm² at 260° C.     

Uniformity and high temperature performance of X-band nitride power HEMTs fabricated from 2-inch epitaxy

X-band performance, high temperature D.C. operation and uniformity have been evaluated for 1 μm gate AlGaN/GaN HEMTs grown by RF atomic nitrogen plasma MBE. Deposition and fabrication were performed on 2-inch (0001) sapphire substrates to determine process uniformity. HEMTs with 300 μm total gate width and dual gate finger geometry have been fabricated with 650–700 cm² V⁻¹×s mobility. Maximum frequency cut-offs on the order of 8–10 GHz were achieved. D.C. performance at room temperature was >500 mA mm⁻¹, and external transconductance was >70 mS mm⁻¹. The transistors operated at test temperatures of 425°C in air.     

Characterization of phosphorus implanted low pressure chemical vapor deposited polycrystalline silicon

Thin (3000–5000Å) low pressure chemically vapor deposited (LPCVD) films of polycrystalline silicon suitable for microelectronics applications have been deposited from silane at 600°C and at a pressure of 0.25 Torr. The films were phosphorus implanted at 150 KeV and electrically characterized with the annealing conditions and film thickness as parameters, over a resistivity range of four orders of magnitude (10³–10⁷Ω/□). Annealing during silox deposition was found to result in a lower film resistivity than annealing done in nitrogen atmosphere. Resistivity measurements as a function of temperature indicate that the electrical activation energy is a linear function of 1/N(N is the doping concentration), changing from 0.056 eV for a doping concentration of 8.9 × 10¹⁸ cm⁻³ to 0.310 eV for doping concentration of 3.3 × 10¹⁸ cm⁻³. The grain boundary trap density was found to have a logarithmically decreasing dependence on the polysilicon thickness, decreasing from 1.3 × 10¹³ cm⁻² for 2850Å polysilicon film to 8.3 × 10¹² cm⁻² for 4500Å polysilicon film.     

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.     

n-Channel AlSb/GaSb modulation-doped field-effect transistors

We report the first fabrication of a GaSb n-channel modulation-doped field-effect transistor (MODFET) grown by molecular beam epitaxy. The modulation-doped structure exhibits a room temperature Hall mobility of 3140 cm² V⁻¹ s⁻¹ and 77 K value of 16000 cm² V⁻¹ s⁻¹, with corresponding sheet carrier densities of 1.3 × 10¹² cm⁻² and 1.2 × 10¹² cm⁻². Devices with 1 μm gate length yield transconductances of 180 mS mm⁻¹ and output of 5 mS mm⁻¹ at 85 K. The device characteristics indicate that electron transport in the channel occurs primarily via the L-valley of GaSb above 85 K. The effective electron saturation velocity is estimated to be 0.9 × 10⁷ cm s⁻¹. Calculations show that a complementary circuit consisting of GaSb n- and p-channel MODFETs can provide at least two times improvement in performance over AlGaAs/GaAs complementary circuits.     

Avalanche breakdown voltage of GaAs hyperabrupt junctions

The avalanche breakdown voltage of a GaAs hyperabrupt junction diode is calculated by using unequal ionization rates for electrons and holes, and shown graphically as a function of the parameters which characterize the impurity profile of the diode. The breakdown voltage decreases abruptly at the critical point of the characteristic length L_c which varies in accordance with the impurity concentration N₀ at X = 0. For example, the critical length L_c is 7.7 × 10⁻⁶ cm and 3.3 × 10⁻⁵ cm for N₀ = 1 × 10¹⁸ cm⁻³ and 1 × 10¹⁷ cm⁻³, respectively. The breakdown voltage of a diode with extremely short or long characteristic length can be estimated from the results for corresponding abrupt junctions. The experimental results agree well with the calculated ones.     

Simulation and experimental results on the forward J–V characteristic of Al implanted 4H–SiC p–i–n diodes

In this work the forward J–V characteristics of 4H–SiC p–i–n diodes are analysed by means of a physics based device simulator tuned by comparison to experimental results. The circular devices have a diameter of 350 μm. The implanted anode region showed a plateau aluminium concentration of 6×10¹⁹ cm⁻³ located at the surface with a profile edge located at 0.2 μm and a profile tail crossing the n-type epilayer doping at 1.35 μm. Al atom ionization efficiency was carefully taken into account during the simulations. The final devices showed good rectifying properties and at room temperature a diode current density close to 370 A/cm² could be measured at 5 V. The simulation results were in good agreement with the experimental data taken at temperatures up to about 523 K in the whole explored current range extending over nine orders of magnitude. Simulations also allowed to estimate the effect of a different p⁺ doping electrically effective profile on the device current handling capabilities.