Energy levels and degeneracy ratios for magnesium in n-type silicon

The energy levels and degeneracy ratios of magnesium in n-type silicon have been determined by Hall effect measurements with the least square method. Magnesium ions appear to occupy two different sites and show different electrical properties. The first is amphoteric and exhibits an acceptor level at E_c ? 0.115 eV (±0.002 eV), degeneracy ratio γ_I^? = 2.5 as well as a donor level at E_c ? 0.40 eV (±0.01 eV), γ_III⁺ = 1. The second exhibits a donor level at E_c ? 0.227 eV (±0.004 eV), degeneracy ratio $\text{γ}{}_{\mathrm{II}}{}^{\mathrm{+}}\text{=}\text{1}\text{2.5}$. The physical nature of these Mg associated site is unknown.     

Determination of Si-metal work function differences by MOS capacitance technique

Very accurate and reliable values of the difference between silicon electron affinity, χ_Si, and the metal work function, Φ_M, have been obtained for seven different metals by the MOS flat-band capacitance technique. Different MOS structures with the same interface charge density and the same metal but varying oxide thickness were manufactured on the same wafer by employing a small temperature gradient during steam oxidation in an r.f. induction heated vertical furnace. The flat-band voltage, V_FB, vs oxide thickness, t_ox, graphs obtained are very good straight lines. Use of both p- and n-Si in case of the metals Au and Cr produced two values of the silicon bandgap E_G. The value of E_G obtained in case of Au differed from the established value of 1·11 eV at room temperature by ?0·04 eV only, and by 0·07 eV in case of Cr. This gives an indication of the experimental accuracy of the Φ_HS = Φ_M ? χ_Si values. $\text{Φ}{}_{\mathrm{MS}}{}^1$ obtained by this technique is 0·73 eV for Ag. ?0·11 eV for Al, 0·82 eV for Au, ?0·06 eV for Cr, 0·63 eV for Cu, ?1·05 eV for Mg, and ?0·82 eV for Sn. The total inaccuracy is limited to $\text{?0.06}\text{+0.03}\text{eV}$.     

Rhodium and iridium as deep impurities in silicon

Rh is found to have two levels—an acceptor at E_c ?0·353 eV and a donor at E_c ?0·591 eV. These are present in equal concentrations but may not correspond to the same site. The hole lifetime for n-type Si diffused with Rh at 1100° is found to be 4·8 × 10^?9 sec.For diffused and quenched Si, Ir produces two levels, a donor at E_c ?0·385 eV (with an unusually large electron capture cross section 10^?10 cm²) and an acceptor at E_c ?0·629 eV. These two levels are inferred to be on different atomic sites. The lifetime for n-Si diffused with Ir at 1100°C is found to be 8·8 × ?10^?9 sec.     

Energy levels and concentrations for platinum in silicon

The energy levels and electrically active concentrations of platinum in silicon have been measured by Hall techniques. Analysis shows platinum to have two electrically active sites. The usual site N_PtI (assumed to be substitutional) predominates (>80%) and has two levels, a donor at E_v+0·28 eV, degeneracy γ_I⁺=2 in p-type material and an acceptor at E_c ?0·20 eV, $\text{γ}{}_{\mathrm{<mtext>I</mtext>}}{}^{\mathrm{?}}\text{=}\text{1}\text{6}$, in n-type material. However a second platinum site exists, and is present to a concentration N_PtII of about 10 per cent with an acceptor level at $\text{E}{}_{\mathrm{<mtext>v</mtext>}}\text{+ 0·42}\text{eV}\text{(γ}{}_{\mathrm{<mtext>II</mtext>}}\text{=}\text{1}\text{8}\text{)}$. The physical nature of this Pt associated site is unknown.Neutron activation analysis has been used to determine total atomic platinum concentrations for diffusions from 800 to 1250°C. These results, in conjunction with Hall measurements, show the electrical activity to be very high. Previous studies on platinum are reviewed and compared to the result of this work.     

Thermal emission rates and capture cross-section of majority carriers at titanium levels in silicon

The thermal emission rates and capture cross-sections of majority carriers on the titanium associated levels in the depletion region of reverse biased silicon p⁺n and n⁺n junctions have been investigated using the admittance spectroscopy technique and the dark capacitance transient method. We have found three levels associated with titanium in silicon. Its thermal activation energies are E_c ?238 ± meV, E_c ?512 ± 5 meV and E_v + 320 ± 5 meV.For the E_c ?238 meV and E_v + 320 meV levels, the thermal capture cross-sections are independent of the temperature: σ_n = 1.01 × 10^?4 cm² and σ_p = 1.55 × 10^?15 cm². The electron capture cross-section on the E_c ? 512 meV levels shows a slight dependence with the temperature, $\text{σ}{}_{\mathrm{n}}\text{= 2.01 × 10}{}^{\mathrm{?16}}\text{(}\text{T}\text{300}\text{)}{}^{\mathrm{?(0.35\pm 0.1)}}\text{cm}{}^2$ in the [120–240 K] range, which can account for the nonradiative multiphonon emission process.     

Use of a Schottky barrier to measure impact ionization coefficients in semiconductors

The use of a Schottky barrier to determine the impact ionization coefficients of electrons and holes in semiconductors has been studied analytically and also evaluated experimentally by comparing the results for silicon with those already available in the literature.The Schottky barrier offers several advantages over a diffused p-n junction in such measurements. Pure electron initiation and pure hole initiation can be separately achieved. The abrupt barrier provides an accurately known electric field, and the linearity of the field distribution simplifies the problem of extracting the ionization coefficients from the multiplication data.We present a general solution of the charge multiplication equation and derive expressions for the ionization coefficients for the particularly simple conditions that can be achieved in a Schottky-barrier junction. Our results for silicon in the range 2 × 10⁵ < E < 4 × 10⁵V/cm can be expressed in the form $\text{α = α}{}_{\mathrm{\infty }}\text{exp}\text{(}\text{?b}{}_{\mathrm{n}}\text{E}\text{)}$ for electrons and $\text{β = β}{}_{\mathrm{\infty }}\text{exp}\text{(}\text{?b}{}_{\mathrm{p}}\text{E}\text{)}$ for holes, with α_∞ = 9·2 × 10⁵ cm^?1, β_∞ = 2·4 × 10⁵ cm^?1, b_n = 1·45 × 10⁶ V/cm and b_b = 1·64 × 10⁶ V/cm.     

The small signal admittance of carbon implanted p-n diodes

In this paper we consider, in detail, how the introduction of radiation damage centres, produced by the implanation of carbon ions, affects the small signal admittance of silicon p-n diodes. Thermally stimulated capacitance measurements are used to obtain the charge states and activation energies of the damage centres. For carbon doses between 1 × 10¹¹ cm^?2 and 1 × 10¹² cm^?2 two trapping levels are observed with activation energies of E_t?E_v=0·31 eV and E_c?E_t=0·37 eV, and for doses between 5 × 10¹² cm^?2 and 5 × 10¹³ cm^?2 an extra level appears with an energy of E_c?E_t=0·25 eV. A study is made of the effects of these damage centres on the small signal capacitance and conductance of the diodes under forward bias. The results are interpreted in terms of a conductivity modulation effect, and it is proposed that this technique yields valuable information on the profile of the damage centres.     

Electric field dependence of mobility fluctuation 1/f; noise in elemental semiconductors

It is shown that Bosman's empirical formula α(E) = α(0)/[1 + (E/E_c′)²] for the field dependence of Hooge's parameter can be explained if it is assumed that only the low-field value μ_aco of the acoustical mobility μ_ac fluctuates and that $\text{μ}{}_{\mathrm{ac}}\text{= μ}{}_{\mathrm{aco}}\text{[1 + (E/E}{}_{\mathrm{c}}\text{′)}{}^2\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$.     

Defect levels in chromium-doped silicon

The transient capacitance technique has been used to study the chromium-related levels in the silicon band gap. Chromium was diffused at temperature of 1100 and 1150°C for 0.5 and 3 hr. Five different levels at E_c?0.11 eV, E_c?0.21 eV, E_c?0.28 eV, E_c?0.36 eV and E_c?0.45 eV were obtained from the Arrheniu plots of the electron thermal-emission rates. The number of levels in the upper half of the band gap decreased from five to two with an increase of Cr-diffusion period. Two levels were located at E_c?0.20 eV (donor) and E_c?0.43 eV (acceptor). A donor level was also observed at E_v + 0.25 eV. The donor level was not affected by the diffusion condition. The majority carrier capture cross sections of the three dominant levels have been measured by the transient capacitance technique modified by the pulse transformer. The values were σ_n = 4.1 × 10^?15 cm² for the upper donor at E_c?0.20 eV, σ_n = 2.0 × 10^?16 cm² for the acceptor at E_c ?0.43 eV and σ_p = 9.1 × 10^?18 cm² for the lower donor at E_v + 0.25 eV, and were independent of temperature. The three dominant levels are due to distinct chromium centers.     

Lead telluride-lead tin telluride heterojunction diode array

PbTePb_0·80Sn_0·20Te heterojunction diode arrays have been fabricated from layers grown by the liquid phase epitaxy technique on Pb_0·80Sn_0·20Te substrates. The quality of grown surfaces was found to be dependent upon crystal orientation and substrate surface treatment. Constitutional supercooling has not been identified as a contributing factor. From the capacitance data, an inversion layer is believed to exist at the PbTePbSnTe interface. The diodes exhibit external quantum efficiencies ranging from 15 to 35 per cent without an anti-reflection coating. Junction zero bias impedances vary from 3 to 7 kΩ for a diode are of 6 × 10^?4 cm², yielding R₀A products from 1·8 to 4·2 Ω-cm². The average for an 18-element array is $\text{2·3 × 10}{}^{10}\text{cm Hz}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{/W}$ for 180°FOV a 300°K background.     

The C-V characteristics of Schottky barriers on laboratory grown semiconducting diamonds

Measurements of the differential capacitance of evaporated gold Schottky barriers on laboratory-grown, boron-doped semiconducting diamonds have been obtained for the first time as functions of reverse-bias voltage, frequency, and temperature. The data are analyzed on the basis of a model which includes the effects of long time constants for hole capture from the deep (boron) level, as well as previously unobserved effects due to the series resistance of the bulk. The barrier height at 300°K is found to be $\text{1·73 ± 1·10}\text{eV}$, in good agreement with the ‘one-third band gap’ value of Mead and Spitzer. Excellent correlation is found between optical transmission measurements and the $\text{C-V}$ analysis for the uncompensated boron concentration, indicating that all of the optically observable dopant is electrically active. By fitting the model with two adjustable parameters at room temperature, good agreement is obtained between measured and calculated capacitance over two and a half decades as a function of temperature. The analysis indicates that the activation energy of the acceptor level is 0·26–0·37 eV for the samples studied, while the associated capture cross-sections are 0·9–2·0 × 10^?17 cm².     

Diffusion of chromium into epitaxial gallium arsenide

Diffusion of Cr into epitaxial GaAs in an open system in the temperature range of 750–850°C was studied. Temperature dependences of the diffusion coefficient and solubility of Cr in GaAs were determined. Temperature dependences of the diffusion coefficient and solubility of Cr are described by the Arrhenius equation with the parameters D ₀ = 1.9 × 10⁹ cm²/s and E = 4.1 ± 0.2 eV for the diffusion coefficient and N ₀ = 2.3 × 10²⁴ cm^?3 and E ₀ = 1.9 ± 0.4 eV for solubility. The effect of protective SiO₂ filmon the Cr diffusion coefficient and morphology of the GaAs surface after diffusion was studied.     

Sequence test method for reliability evaluation of semiconductor devices

The failure-rate λ, of a device can be determined using Arrhenius model $\text{λ = A}\text{e}{}^{\mathrm{<mtext>?E</mtext><mtext>KT</mtext>}}$. The number of thermal cycles a device can withstand can be postulated using an exponential model, N = g e^?aT. Based on these models, a “sequence” process of thermal-fatigue and life tests is arrived at, which makes use of a mathematical equation giving the rate of decay of MTBF relative to the number of thermal-cycles, $\text{δ = P}\text{exp}\text{[p · ΔT + (}\text{q}\text{T}\text{)]}$. In other words, MTBF of the devices can be reduced by pre thermal cycling.     

Diffusion of chromium in GaAs under equilibrium arsenic-vapor pressure

The diffusion of chromium in GaAs is studied under equilibrium arsenic-vapor pressure. The temperature dependences of chromium diffusivity and solubility in GaAs are determined. These dependences are described by the Arrhenius equation with the parameters D ₀ = 3.1 × 10⁵ cm²/s and E = 3.2 ± 0.4 eV for the diffusivity and N _S = 2.1 × 10²¹ cm^?3 and E _S = 1.0 ± 0.3 eV for the solubility. The obtained experimental results are compared with our previously published data on the diffusion of chromium under high arsenic-vapor pressure and analyzed in terms of the dissociative mechanism of migration of chromium in GaAs.     

Electron temperature dependences of nonradiative multiphonon hot-electron capture coefficients of deep traps in semiconductors—I: Small lattice relaxation

Generalizing the theory of nonradiative multiphonon capture of thermal electrons for cases where the effective temperature T_e of conduction electrons differs from lattice temperature T_L, we develop a corresponding theory of hot electron capture. Its principal novelty is due to an exponential decrease ∝ exp(?E/k_Bτ) of the efficiency of this energy loss mechanism, at increasing electron energy E, for the usual regime of small lattice relaxation characterized by a corresponding “capture extinction temperature” τ. The resulting T_e-dependences of hot electron capture coefficients at sufficiently low T_e (

τ, i.e. in the “Sommerfeld factor regime”) are controlled by the net charge of the centre which means C(T_e) ∝ C(T_e) ∝ $\text{T}{}_{\mathrm{e}}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$, ∝ T_e⁰, or ∝ $\text{T}{}_{\mathrm{e}}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ exp$\text{[?3·(θ/T}{}_{\mathrm{e}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{]}$ in cases of attraction, neutrality, and repulsion, respectively. At high T_e

τ, i.e. in the “energy-loss factor regime”) these relations reduce to the form C(T_e) ∝ $\text{T}{}_{\mathrm{e}}{}^{\mathrm{<mtext>?</mtext><mtext>3</mtext><mtext>2</mtext>}}$ which is simply due to an increasing depopulation of the relevant region of low-lying band states. This theory is applied to electron capture by a singly charged repulsive gold centre and a doubly charged repulsive copper centre in germanium. The corresponding theoretical maximum values C_max.^(?1) = 5.2 · 10^?11 cm³ s^?1 and ifC_(rnmax.)^(?2) = 2.4 · 10^?12 cm³ s^?1 of hot electron capture coefficients are in good agreement with experimen observations.     

Thermal noise measurements on space-charge-limited hole current in silicon

Silicon pvp devices were manufactured whose d.c. and a.c. properties conform closely to the simple model of trap-free space-charge-limited current (sclc) of holes. Room temperature measurements of the spectral density of the noise from 10 kHz to 10 MHz at various operating points reveal a white noise component whose value is given by $\text{S}{}_{\mathrm{v}}\text{ 〈Δν}{}^2\text{〉 Δ? = β · 4kT (V/I),}\text{where}\text{β = 1.0±6\%}$, and V/I is the d.c. resistance of the device at the operating point. At high operating points, where the d.c. characteristic agrees quantitatively with the dependence $\text{J = (}\text{9}\text{8}\text{)??}{}_0\text{μV}{}^2\text{/W}{}^3$ of pure sclc, the results reduce to S_i = α · 4kT (?I/?V), with α = 2.0±7%.     

A Study of Deep Defect Levels in Semi-Insulating SiC Using Optical Admittance Spectroscopy

Optical admittance spectroscopy (OAS), supported by electron paramagnetic resonance (EPR) measurements, is used to identify the controversial vanadium acceptor levels in vanadium-doped semi-insulating (SI) 4H-SiC and 6H-SiC. The V^3+/4+ levels for the cubic site are likely located at E _c − 0.67 ± 0.02 eV and E _c − 0.70 ± 0.02 eV in 6H-SiC and E _c − 0.75 ± 0.02 eV in 4H-SiC. A peak at 0.87 ± 0.02 eV in the 6H-SiC is tentatively assigned to the same transition at the hexagonal site and the associated transition in 4H-SiC is thought to occur near 0.94 eV. All assignments are supported by the observation of V³⁺ in the EPR spectrum.     

Samarium-atom adsorption and desorption on iridium

The adsorption and condensation of samarium on Ir(111) are investigated by thermionic emission spectroscopy and thermal desorption spectroscopy (TDS). During Sm deposition, the work function is found to fall monotonically from 5.8 to 2.7 eV and then to rise slowly to a plateau at 2.9 eV, for any substrate temperature from the range 700–1200 K. The optimal Sm coverage is estimated at 0.51 ± 0.03. The activation energy E⁺ and the preexponential factor C for Sm-ion desorption and those for Sm-atom desorption, E₀ and D, respectively, are determined in the temperature range 1800–2050 K and at a coverage small enough not to alter the work function of the iridium. Their values are as follows: E⁺ = 5.72 ± 0.10 eV, E⁺ = 5.72 ± 0.10 eV, D ～ 1 × 10¹³s^?1, and C ～ 1.3 × 10¹³ s^?1. Several Sm phases are detected in each TDS peak.     

Growth of CdGeAs2 single crystals by the chemical vapor transport method

We have grown CdGeAs₂ single crystals by chemical vapor transport (CVT), a method not previously applied for this compound. The crystallographic data of this chalcopyrite (cell parametersa ₀ = 5.9456 ± 0.0001Å, c₀ = 11.2131 ± 0.0007Å) and its electrical transport properties are reported. Predominantly n-type crystals are obtained (at RTn = 1 · 10¹⁷cm?3, μⁿ = 2000 cm²(Vs)^?1). Vacuum heat treatment at 500° C yields a type conversion fromn- to p-type. In all p-type samples the minority carrier mobility is calculated to be larger than 10000 cm²(Vs)^?1.