Circular and linear enhancement-mode 6H-SiC MOSFETs for high temperature applications

Direct current measurements are performed up to 673K at circular and linear (shown in parenthesis) enhancement-mode metal oxide semiconductor field effect transistors (MOSFETs). These devices are fabricated on a p-type 6H-SiC epitaxial layer with a doping concentration N_A ≈ 1 × 10¹⁶ cm⁻¹. The n⁺ source/drain regions and the p⁺ regions for the channel stops are achieved by ion implantation of nitrogen and aluminum, respectively. Both MOSFET geometries show excellent output characteristics with a good saturation behavior even at elevated temperatures. The inversion layer mobility μ_n extracted in the linear region is 38 cm²·V⁻¹·s⁻¹ (35 cm²·V⁻¹·s⁻¹) and reveals a weak dependence on temperature with a maximum of 46 cm²·V⁻¹·s⁻¹ (42 cm²·V⁻¹·s⁻¹) at about 473K. Regarding the transfer characteristics, the drain current I_D can be well modulated by the gate-source voltage V_GS resulting in an I_on/L_off-ratio of 10⁸ (10⁸) at 303K and 10⁵ (10⁶) at 673K. In the subthreshold regime, I_D can be pinched off well below 10 pA with a subthreshold swing of 150 mV/decade (155 mV/decade) at room temperature. The threshold voltage V_T as a function of temperature shows two linear sections with negative temperature coefficients of −6.8 mV·K⁻¹ (−6.8 mV·K⁻¹) from 303 to 423K and −2.5 mV·K⁻¹ (−2.0 mV·K⁻¹) from 423 to 673K. By measuring V_T as a function of bulk-source voltage V_BS at different temperatures, N_A can be directly estimated at a transistor and gives 9.6 × 10¹⁵ cm⁻³ (9.8 × 10¹⁵ cm⁻³). The measured bulk Fermi potential Φ_f of the p-type epitaxial layer deviates less than 10% from the calculated value at a given temperature.     

Frequency bandwidth and conversion loss of a semiconductor heterodyne receiver with phonon cooling of two-dimensional electrons

The temperature and concentration dependences of the frequency bandwidth of terahertz heterodyne AlGaAs/GaAs detectors based on hot electron phenomena with phonon cooling of two-dimensional electrons have been measured by submillimeter spectroscopy with a high time resolution. At a temperature of 4.2 K, the frequency bandwidth at a level of 3 dB (f _{3 dB}) is varied from 150 to 250 MHz with a change in the concentration n _s according to the power law f _3dB ∝ n _s ^−0.5 due to the dominant contribution of piezoelectric phonon scattering. The minimum conversion loss of the semiconductor heterodyne detector is obtained in structures with a high carrier mobility (μ > 3 × 10⁵ cm² V⁻¹ s⁻¹ at 4.2 K).     

Influence of fast-neutron irradiation on the intensity of the copper-related luminescence band at hν m =1.01 eV in n-type GaAs

The influence of neutron irradiation (the energy E=2 MeV and the dose Φ=10¹³–10¹⁵cm⁻²) and subsequent anneals (the annealing temperature T _a =400–700 °C and the annealing time is 30 min) of n-type GaAs(Te,Cu) crystals with an initial carrier concentration n ₀=2×10¹⁸ cm⁻³ on the intensity of the copper-related luminescence band with an emission maximum at hν _m =1.01 eV is studied. A significant irradiation-induced increase in the intensity of the band is observed. It is attributed to a radiation-stimulated increase in the concentration of emitting centers (Cu_Ga V _As pairs) as a result of the effective interaction of interstitial copper atoms with irradiation-induced gallium (V _Ga) and arsenic (V _As) vacancies, as well as V _Ga V _As divacancies. Fiz. Tekh. Poluprovodn. 31, 1171–1173 (October 1997)     

Microstructure coarsening during static annealing of 60Sn40Pb solder joints: III intermetallic compound growth kientics

The growth of the total (Cu₃Sn+Cu₆Sn) intermetallic compound layer in Cu-60Sn40Pb solder joints during static annealing at 50°C to 150°C was described by the equation hi=h_o+A_o exp(−Q_a/RT)t^p with h_o=0–0.3 μm, p=0.38–0.70, A_o=1.9×10⁻⁴–3.4×10⁻⁴ m/s^p, and Q_a=25.5–30.9 kJ/mole. These constants are within the range of those obtained by others and give values of D_o and Q which are in reasonable accord with those for the diffusion coefficients in Cu₃Sn and Cu₆Sn₅ determined in diffusion couples. The deviation of the values of the time exponent p from the ideal of 0.5 for diffusion growth may be due to inaccuracies or errors pertaining to the measured thickness (especially h_o) and the complex nature of the diffusion process.     

Effects of High-Energy Electron Irradiation on ZnO/Si MSM Photodetectors

ZnO/Si metal–semiconductor–metal photodetectors (MSM-PDs) were subjected to high-energy electron irradiation (HEEI) to total fluence of 2 × 10¹³ cm⁻². ZnO/Si MSM-PDs demonstrated at least 43% greater radiation resistance than similar Si devices. Room-temperature annealing of radiation damage was observed as 63% recovery of photocurrent over 47 days. The current transport mechanism for ZnO/Si MSM-PDs was dominated by space-charge-limited conduction (SCLC) with minimal effect on conduction regime due to HEEI. Analysis of photoluminescence (PL) data indicates that the radiation-induced defects are likely oxygen and zinc vacancies, i.e., (V₀⁺) and (V_Zn ^- - H ⁺ )⁰ (\hbox{V}_{\rm{Zn}}^{ - } - \hbox{H}^{ + } )^{0} , respectively.     

The annealing of Cd1−xZnxTe in CdZn vapors

As-grown CdZnTe usually contains defects, such as twins, subgrain boundaries, dislocations, and Te precipitates. It is always important to anneal CdZnTe slices in Cd vapor to eliminate these defects, especially Te precipitates. The exchange of Zn atoms between the slices and the vapor plays an important role during the annealing process. In this paper, the effects of Zn partial pressure on the properties of the annealed slices are studied carefully by measuring the concentration profiles, the infrared (IR) transmission spectra, and the x-ray rocking curves. It was found that a surface layer with different compositions and possibly different structure from the bulk crystal formed during the annealing of CdZnTe samples in the saturated Zn vapor. The accumulation of excess Te in the surface layer helps to increase the IR permeability of the bulk crystal greatly. To improve the crystallization quality, a lower Zn-pressure annealing should be used following the high Zn-pressure annealing. The diffusion of Zn in the bulk crystal has also been analyzed at the temperatures of 700°C and 500°C. Calculations determined that D_Zn (700°C)=4.02 × 10⁻¹² cm²s⁻¹ and D_Zn (500°C)=1.22 × 10⁻¹³ cm²s⁻¹.     

Characterization of Hg0.7Cd0.3Te n- on p-type structures obtained by reactive ion etching induced p- to n conversion

This paper presents transport measurements on both vacancy doped and gold doped Hg_0.7Cd_0.3Te p-type epilayers grown by liquid phase epitaxy (LPE), with N_A=2×10¹⁶ cm⁻³, in which a thin 2 μm surface layer has been converted to n-type by a short reactive ion etching (RIE) process. Hall and resistivity measurements were performed on the n-on-p structures in van der Pauw configuration for the temperature range from 30 K to 400 K and magnetic field range up to 12 T. The experimental Hall coefficient and resistivity data has been analyzed using the quantitative mobility spectrum analysis procedure to extract the transport properties of each individual carrier contributing to the total conduction process. In both samples three distinct carrier species have been identified. For 77 K, the individual carrier species exhibited the following properties for the vacancy and Au-doped samples, respectively, holes associated with the unconverted p-type epilayer with p ≈ 2 × 10¹⁶ cm⁻³, μ ≈ 350 cm²V⁻¹s⁻¹, and p ≈ 6 × 10¹⁵ cm⁻³, μ ≈ 400 cm²V⁻¹s⁻¹; bulk electrons associated with the RIE converted region with n ≈ 3 × 10¹⁵cm⁻³, μ ≈ 4 × 10⁴ cm²V⁻¹s⁻¹, and n ≈ 1.5 × 10¹⁵ cm⁻³, μ ≈ 6 × 10⁴ cm²V⁻¹s⁻¹; and surface electrons (2D concentration) n ≈ 9 × 10¹² cm⁻² and n ≈ 1 × 10¹³ cm⁻², with mobility in the range 1.5 × 10³ cm²V⁻¹s⁻¹ to 1.5 × 10⁴ cm²V⁻¹s⁻¹ in both samples. The high mobility of bulk electrons in the RIE converted n-layer indicates that a diffusion process rather than damage induced conversion is responsible for the p-to-n conversion deep in the bulk. On the other hand, these results indicate that the surface electron mobility is affected by RIE induced damage in a very thin layer at the HgCdTe surface.     

Self-Diffusion in gallium arsenide

The self-diffusion of arsenic in gallium arsenide has been studied over the temperature range 1000 to 1075δC using radiotracer techniques.⁷⁶As was diffused into GaAs samples at known arsenic pressures in sealed capsules. After diffusion, layers were removed from the surface using anodic oxidation followed by oxide dissolution. Diffusion profiles were obtained by measuring the⁷⁶As concentration in each sectioned layer by γ-radiation counting. Diffusion coefficients at P_{As 2} = 0.75 atm and over the temperature range 1000 to 1050δC were found to be 5.2 × 10^-16cm²s^-1 to 1.5 × 10^-15 cm²s^-1, leading to an activation energy of the order of 3.0^± 0.04 eV and a pre-exponential factor of 5.5 × l0^-4 ± 2.4 × 10^-4 cm²s^-1. Diffusion coefficients at P_{As 2} =3.0 atm were found to be 5.5 × 10^-15 and 9.8 × 10^-16 cm² s^-1 at 1050 and 1075δC, respectively. Results are discussed in terms of native point defect equilibria with the arsenic gaseous phase, and with respect to other work. It is deduced from our observed arsenic pressure dependence of the arsenic diffusivity that the most likely diffusion mechanism     

The temperature and pressure dependence of the electron and hole mobilities in GaxIn1-xAsyP1-y alloys

A wide range of samples of both n-type and p-type Ga_xIn_1-xAs_yP_1-y on InP has been grown by LPE with carrier concentrations in the low 10¹⁶cm⁻³range. The electron mobility (μ_e) at room temperature decreased from about 4000 cm²V⁻¹s⁻¹ at y = 0 and passed through a shallow minimum near y = 0.25. At high y values, μ_e rose steeply, reaching 11 000 cm²V⁻¹s⁻¹ at the ternary boundary. In the p-type material the hole mobility (μ_p) varied from 140 cm V⁻¹s⁻¹ in InP, passed through a minimum of about 70 cm²V⁻¹s⁻¹ near y = 0.5 and then increased swiftly towards the ternary boundary. The temperature dependence of both μ_e and μ_p suggested the presence of alloy or space-charge scattering. In order to distinguish between these two mechanisms the pressure coefficient of the direct band-gap dE_o/dP was measured as a function of y by observing the movement with pressure of the photoconductive edge. From dE_o/dP the pressure variation of the effective mass was deduced. By measuring the change in electron and hole mobilities with pressure, it was then possible to establish that alloy scattering rather than space-charge scattering was occurring. From the composition dependence of the alloy scattering potentials for electrons and holes predictions have been made of the variation of μ_e and μ_P with temperature, pressure and dopant Presently a Nuffield Science Fellow concentration. At room temperature a maximum electron mobility of about 11,200 cm²V⁻¹ s⁻¹ is indicated. Presently a Nuffield Science Fellow     

Diffusion and solid solubility of Zn in GaP at 850°C

Zinc was diffused at 850°C from ternary sources containing 1–20 atom percent Zn and 0.5–1.0 atom percent P in Ga into n-type GaP grown by liquid phase epitaxy (LPE) and the liquid encapsulated Czochralski (LEC) process. Data on the surface concentration, and thereby the solid solubility of Zn as a function of the source composition, were obtained from⁶⁵Zn radiotracer analysis and electrical measurements. At 850°C these values range from 8×l0¹⁷ cm⁻³ for a 1 atom percent Zn to 5×10¹⁸ cm⁻³ for a 20 atom percent Zn concentration in the Ga/P/Zn ternary solution. These data are self-consistent, although they are somewhat lower than the previously reported values . Qualitatively, the results agree with recent thermodynamic calculations. The diffusion kinetics were found to be non-ideal as indicated by departures from a linear-square-root-of-time model and by reproducible changes in the junction depth following pre-diffusion heat treatments in different ambients.     

Pd/Sb(Zn) and Pd/Ge(Zn) ohmic contacts on p-type indium gallium arsenide: The employment of the solid phase regrowth principle to achieve optimum electrical and metallurgical properties

The development of two metallizations based on the solid-phase regrowth principle is presented, namely Pd/Sb(Zn) and Pd/Ge(Zn) on moderately doped In_0.53Ga_0.47As (p=4×10¹⁸ cm⁻³). Contact resistivities of 2–3×10⁻⁷ and 6–7×10⁻⁷ Ωcm², respectively, have been achieved, where both systems exhibit an effective contact reaction depth of zero and a Zn diffusion depth below 50 nm. Exhibiting resistivities equivalent to the lowest values of Au-based systems in this doping range, especially Pd/Sb(Zn) contacts are superior to them concerning metallurgical stability and contact penetration. Both metallizations have been successfully applied for contacting the base layer of InP/In_0.53Ga_0.47As heterojunction bipolar transistors.     

Implantation of sodium ions into germanium

The donor properties of Na atoms introduced by ion implantation into p-Ge with the resistivity 20–40 Ω cm are established for the first time. Na profiles implanted into Ge (the energies 70 and 77 keV and the doses (0.8, 3, 30) × 10¹⁴ cm⁻²) are studied. The doses and annealing temperatures at which the thermoprobe detects n-type conductivity on the sample surface are established. After implantation, the profiles exhibit an extended tail. The depth of the concentration maximum is in good agreement with the calculated mean projected range of Na ions R _p . Annealing for 30 min at temperatures of 250–700°C brings about a redistribution of Na atoms with the formation of segregation peaks at a depth, which is dependent on the ion dose, and is accompanied by the diffusion of Na atoms to the surface with subsequent evaporation. After annealing at 700°C less than 7% of the implanted ions remain in the matrix. The shape of the profile tail portions measured after annealing at temperatures 300–400°C is indicative of the diffusion of a small fraction of Na atoms into the depth of the sample.     

Optical and Magnetic Properties of ZnO:V Prepared by Ion Implantation

We report on the optical and magnetic properties of the magnetic semiconductor Zn(V)O fabricated by implantation of 195 keV ₅₁V⁺ ions into bulk ZnO:Al grown by a hydrothermal technique. Two sets of the samples, containing N _d –N _a ∼ 10¹⁵ cm⁻³ and 10¹⁸ cm⁻³, were implanted to doses of 1 × 10¹⁵ cm⁻², 3 × 10¹⁵ cm⁻², and 1 × 10¹⁶ cm⁻². The ion implantation was performed at 573 K. To remove irradiation-induced defects, the samples were annealed in air at 1073 K. Photoluminescence (PL) measurements of Zn(V)O films were carried out at temperatures from 10 K to 300 K. The effects of implantation dose and free carrier concentration on the magnetic properties of Zn(V)O were studied using a superconducting quantum interference device magnetometer. Ferromagnetism has been observed in annealed highly conductive samples implanted to 1 × 10¹⁶ cm⁻². The PL studies of ZnO bulk samples implanted with V⁺ have revealed that thermal annealing at 1073 K restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the PL spectrum of the highly conductive samples implanted to the dose of 1 × 10¹⁶ cm⁻², which is most probably due to complexes involving V ions.     

Investigation of 1/<Emphasis Type="Italic">f</Emphasis> Noise Mechanisms in Midwave Infrared HgCdTe Gated Photodiodes

In this work, gated midwave infrared (MWIR) Hg_1–x Cd _x Te photodiodes are used to investigate the physical origin of 1/f noise generation. Gated photodiodes were fabricated on liquid-phase epitaxy p-type HgCdTe MWIR material with a vacancy-doped concentration of 1.6 × 10¹⁶ cm⁻³ and x = 0.31. CdTe was thermally deposited and used as both a passivant and a mask for the plasma-based type conversion, and ZnS was used as an insulator. Fabricated devices show a R ₀ A of 1–5 × 10⁴ Ωcm² with zero gate bias. Application of 2 V to the gate improves the R ₀ A by more than two orders of magnitude to 6.0 × 10⁶ Ωcm², which corresponds to the p-type surface being at transition between depletion and weak inversion. Trap-assisted tunneling (TAT) current was observed at negative gate biases and reverse junction biases. For gate biases greater than 3 V, a field-induced junction breakdown was observed. An I _n = α I ^β f ^−0.5 trend was observed above 200 pA reverse bias dark current, with α = 3.5 × 10⁻⁵ and β = 0.82, which corresponds to the TAT dominated region. Below 200 pA, junction generation-recombination (GR) current starts to dominate and this previously mentioned trend is no longer observed. Junction GR current was not seen to be correlated with 1/f noise in these photodiodes.     

Luminescence and electrical properties of InGaN/AlGaN/GaN light emitting diodes with multiple quantum wells

Luminescence spectra of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures with multiple quantum wells are studied for currents in the range J=0.15 μA-150 mA. The comparatively high quantum efficiency for low J(J _max=0.5–1 mA) is a consequence of a low probability for the nonradiative tunnel current. The current-voltage characteristics J(V) are studied for J=10⁻¹²–10⁻¹ A; they are approximated by the function V=ϕk+mkT· [1n(J/J ₀)+(J/J ₁)^0.5] + J · R _s. The portion of V∞(J/J ₁)^0.5 and measurements of the dynamic capacitance indicate that i-layers adjacent to the active layer play an important role. The spectra are described by a model with a two-dimensional density of states with exponential tails in multiple quantum wells. The rise in T with increasing J is determined from the short-wavelength decay of the spectrum of the blue diodes: T=360–370 K for J=80–100 mA. An emission band is observed at 2.7–2.8 eV from green diodes at high J; this band may be explained by phase separation with different amounts of In in the InGaN. Fiz. Tekh. Poluprovodn. 33, 445–450 (April 1999)     

Photoelectric and luminescent properties of dysprosium-doped silver chloride

The influence of dysprosium doping on the photoelectric and luminescent properties of AgCl crystals is studied by methods of microwave photoconductivity and photoluminescence. Doping affects both the loss kinetics of photogenerated electrons and luminescence spectra and parameters of photostimulated burst of luminescence. It is shown that the charged [Dy_Ag^·· · V′_Ag]^· or neutral [Dy_Ag^·· · 2V′_Ag] ^x complexes are responsible for a new luminescence band peaked at 470 nm, which manifests itself at weight concentrations of the doping additive >10⁻⁶%. The long-wavelength shoulder at 570 nm in the photoluminescence spectra is attributed to intracenter transitions in the Dy³⁺ ions. The rate constant of the reaction of electron capture into the traps forming upon introduction of the dopant, k _t = (3–5) × 10⁻⁸ cm³ s⁻¹, is evaluated. It is assumed that the traps are Dy³⁺ dysprosium ions.     

Nature of E c −0.37 eV centers and the formation of high-resistivity layers in n-type silicon

The DLTS and Van der Pauw methods are used to investigate the production of E _c −0.37 eV centers responsible for the formation of high-resistivity layers in n-type Si irradiated with electrons and annealed in the temperature range 80–320 °C. An analysis of the experimental data leads to a conclusion as to the composition of the E _c −0.37 eV centers ([V-O-C]) and to the conclusion that their formation is stimulated by a flux of interstitial atoms away from the interface into the interior of the semiconductor during annealing accompanied by the reactions: 1) I+C_s→C_i,C_i+[V-O]→[V-O-C] (dominant reaction); 2) I+V ₂→V,V+[C-O]→[V-O-C]. Fiz. Tekh. Poluprovodn. 31, 993–997 (August 1997)     

The use of secondary ion mass spectrometry in the study of matrix atom diffusion in epitaxial CdTe

The self-diffusion of Cd and Te in liquid phase epitaxially grown CdTe layers has been studied using stable isotopes of Cd¹⁰⁸ and Te¹²². A two layer structure was grown from In solutions at 300–250° C, with the first layer being normal CdTe and the second enriched in Cd₁₀₈ and Te¹²². Secondary ion mass spectrometry was used to measure the concentration of the Cd and Te species as a function of depth in the as-grown structure and after heat treatment at 500° C. The main result was that after heating, no movement of Te could be detected. However, the Cd had diffused rapidly both at the solidsolid epilayer interface and at the solid-vapour interface. The self-diffusion coefficient for Cd in CdTe calculated from this data was D^500° _cd ˜ 3 ± 1 × 10¹³cm²s^-1 in reasonable agreement with published data.     

The epitaxial growth of ZnO on sapphire and MgAl spinel using the vapor phase reaction of Zn and H2O

The gas phase reaction of Zn and H₂O in a He carrier gas has been used as the basis for the chemical vapor deposition of ZnO on sapphire and MgAl spinel. Deposit characteristics were studied as a function of reactor linear gas stream velocity, Zn/H₂O vapor phase ratio, temperature and substrate preparation. It was round that the substrate support can influence the surface morphology significantly and that in situ pretreatment can affect epitaxial relationships between deposit and substrate. Transparent, visually smooth deposits of (11–24) ZnO can be obtained on chemically polished (0001) sapphire at 815°C using average linear gas stream velocities, ν, of 6-12 cm/sec referenced to room temperature in conjunction with a Zn/H₂O reactor input-pressure ratio of 0.02–0.09 (using Zn reactor pressures of 1.2–5.0 × 10⁻³ atm) . The substrates are given an H₂O in situ pretreatment at 900°C prior to deposition at ν = 3 cm/sec with the partial pressure of H₂O in He = 5.7 × 10 atm.     

Conductivity compensation in <Emphasis Type="Italic">p</Emphasis>-6<Emphasis Type="Italic">H</Emphasis>-SiC in irradiation with 8-MeV protons

Carrier removal rate (V _d ) in p-6H-SiC in its irradiation with 8-MeV protons has been studied. The p-6H-SiC samples were produced by sublimation in vacuum. V _d was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that complete compensation of samples with initial value of N _a − N _d ≈ 1.5 × 10¹⁸ cm⁻³ occurs at an irradiation dose of ∼1.1 × 10¹⁶ cm⁻². In this case, the carrier removal rate was ∼130 cm⁻¹.