Copper impurity levels in silicon

This paper presents a new model of copper impurity levels in silicon, and suggests a new method to analyze the parameters of multilevel impurities using Hall data. On the assumption that the energy levels of copper do not depend on the conduction type of silicon and the concentration of copper, an impurity level model which can explain all the Hall data of many different copper-doped silicon samples is proposed using a computer-aided numerical analysis. Experimental data and analysis indicate that copper exists in silicon in the form of four independent species, viz. substitutional species (Cu_I), interstitial species (Cu_IV) and two copper-associated species Cu^II and Cu^III. The usual species Cu^I has three acceptor levels and a donor level below the intrinsic level. Cu^II has two levels, an acceptor and a donor level respectively, below the donor level of Cu^I. Cu^III produces an acceptor level at a slightly distant position from the conduction band edge. That the intersitial species Cu^IV behaves as a shallow donor is well-known, but its behavior is predominant only in samples diffused at temperatures below 900°C because of the precipitation of its species. Not only the energy levels of copper, but also the degeneracy ratios associated with these levels have been simultaneously determined, and it has been indicated that the degeneracy ratios have an important effect on the temperature dependence of the carrier concentration.     

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.     

Photoluminescence of nitrogen-doped zinc selenide epilayers

Photoluminescence (PL) studies of nitrogen doped ZnSe epilayers grown by molecular beam epitaxy have been performed as a function of excitation wavelength, power density, and temperature. The broad emission from heavily doped ZnSe:N is composed of two distinct bands which we label as N_I and N_II. The dominant band N_I appears at 2.54 eV, while the N_II band position is sensitive to excitation power and occurs between 2.55 and 2.61 eV. The N_I emission energy is insensitive to incident power or temperature over the ranges studied. Further, a 69 meV localized phonon of the N_I band is observed. We propose that the N_I band is related to transitions within a (V_se+-Zn-N_se-)0 close-associate pair. The N_II band displays characteristics consistent with the conventional donor acceptor pair model. A third band N_III at 2.65 eV is observed under high-power pulsed excitation. Previous studies of heavily doped ZnSe:N had suggested that the broad emission band was described by a modified donor-acceptor pair model. Our PL study does not support this previous model. In addition, our data suggests that singly ionized selenium vacancy complexes form in heavily doped ZnSe:N and play a role in compensation.     

Characterisation of properties of nickel in silicon using thermally stimulated capacitance method

Detailed TSCAP measurements on silicon P⁺N and N⁺P diodes confirm the existence of two acceptor levels of nickel lying 0.21 ± 0.01 and 0.41 ÷ 0.01 eV from the valence and conduction bands respectively. Concentration of these centers, their spatial distribution and behaviours after several annealing treatments are also presented.     

Structural and luminescent properties of ZnO:P films produced by annealing ZnP<Subscript>2</Subscript> wafers in atomic oxygen

The epitaxial ZnO:P films are fabricated by annealing the ZnP₂ wafers in atomic oxygen (oxygen radicals). The properties of the films are studied by X-ray diffraction analysis, atomic force microscopy, Auger spectroscopy, and photoluminescence measurements. In the X-ray diffraction spectra of the samples, the (002) peak is observed, suggesting that the ZnO:P films are oriented along the c axis. The Auger spectroscopy data show that the ZnO films contain phosphorus. The low-temperature photoluminescence spectrum observed for the ZnO: P films exhibits a 3.356 eV peak presumably corresponding to excitons bound at neutral acceptors and a peak at 3.306 eV (free electron)-acceptor transitions associated with the P_O level. The phosphorus related acceptor level is localized at 128 meV above the top of the valence band. The origin of the 3.312 eV band related to recombination at donor-acceptor pairs is discussed.     

Properties of the CuInS2 surface and the effect of organic layers

This study is devoted to the properties of the CuInS₂ (CIS) surface and the effect of thin organic layers on them. The CIS layers under study feature photosensitivity in the range of 1.5–3 eV. A quadratic approximation of the long-wavelength edge of a spectral dependence of the photovoltage yields the band gap E _g =1.46±0.02 eV. It is shown that the major contribution to the formation of the barrier near the CIS free surface is made by acceptor levels arranged higher than the CIS valence band top by ～0.1 and ～0.2 eV. As a polymeric layer is deposited onto the CIS free surface, the potential barrier height slightly decreases, while the carrier transport efficiency simultaneously increases. As an organic p-type semiconductor is deposited onto the CIS free surface, trapping centers are partially neutralized, and the carrier recombination rate on the CIS film surface decreases.     

Irrelevance of interface defects to heterojunction band offsets

We present a photoemission measurement of the valence band discontinuity, ΔE_v, and the Fermi level, E_F, position at the interface between different surface reconstructions of GaAs(100) and Ge. GaAs(100) exhibits a number of surface reconstructions that differ in their As content and bonding configuration. The initial and final Fermi level position is observed to move toward the conduction band as the As content of the starting surface increases. The observed change in the final E_F due to the variation in surface As content is 0.3 eV. The band offsets are the same (0.46±0.05) regardless of the starting surface. The addition of As during the interface formation causes the Fermi level position to further move toward the conduction bands of Ge and GaAs; however, it doesnot change the band offsets. We conclude that deposition-induced defects do not occur in sufficient density across the interface to play a primary role in determining the GaAs/Ge(100) heterojunction potential step.     

Effects of surface treatment using aqua regia solution on the change of surface band bending of p-type GaN

Effects of surface treatment on the change of band bending at the surface of p-type GaN were studied using synchrotron radiation photoemission spectroscopy, and the results were used to interpret the reduction of contact resistivity by the surface treatment. The contact resistivity on p-type GaN decreased from (5.1±1.2)×10⁻¹ to (9.3±3.5)×10⁻⁵Ω cm² by the surface treatment using aqua regia prior to Pt deposition. Surface band bending was reduced by 0.58 eV and 0.87 eV after the surface treatments by HCl and aqua regia solutions, respectively. The atomic ratio of Ga/N decreased as the photoelectron detection angle was decreased, indicating that the surface oxide was mainly composed of Ga and O, GaO_x, formed during high-temperature annealing for the generation of holes, and Ga vacancies, V_Ga, were produced below the GaO_x layer. Consequently, the aqua regia treatment plays a role in removing GaO_x formed on p-type GaN, leading to the shift of the Fermi level toward the energy levels of V_Ga located near the valence band edge. This causes the decrease of barrier height for the transport of holes, resulting in the good ohmic contacts to p-type GaN.     

Valence band discontinuity of the (0001) 2H-GaN / (111) 3C-SiC interface

X-ray and UV photoelectron spectroscopies were used to measure the valence band discontinuity at the interface between (0001) 2H-GaN films and 3C-SiC (111) substrates. For GaN films grown by NH₃ gas source molecular beam epitaxy on (1×1) 3C-SiC on-axis surfaces, a type I band alignment was observed with a valence band discontinuity of 0.5±0.1 eV. A type I band alignment was also determined for GaN films grown on (3×3) 3C-SiC, but with a larger valence band discontinuity of 0.8±0.1 eV.     

Electrical properties of nickel in silicon

Electrical activity and energy levels as well as diffusion properties of nickel in silicon have not yet been reliably established. In this paper, we investigated the diffusion and the electrical properties of nickel in silicon to confirm that nickel is electrically active and introduces one acceptor and one donor level by combined measurements of Hall coefficient and DLTS, and measurements of the distribution of electrically active nickel in various silicon diodes by DLTS. The former experiments show that bothn- andp- type silicon are compensated by nickel and that nickel introduces an acceptor level ofE _c-0.47 ± 0.04 eV and a donor level ofE _v +0.18 ± 0.02 eV. The concentrations of these two levels are almost identical over the diffusion temperatures from about 800 to 1100° C, indicating that these donor and acceptor levels are due to different charge states of the same nickel center. In the distribution measurements of electrically active nickel in silicon diodes, we inspected how nickel can be observed by DLTS. It was found that the nickel diffusion intop- n junction is rather complicated, the distribution profiles of nickel in the vicinity of thep- n junction being markedly influenced by an additional heating at elevated temperatures after the nickel diffusion. This gives evidence that the difference in silicon devices used in various studies could give rise to different results.     

Determination of bulk trap parameters using thermal dielectric relaxation techniques

A new non-steady-state technique for determining the energy levels of traps through which electron-hole pairs are generated in the depletion-layer of the silicon of metal-oxide-silicon (MOS) capacitor structures has been applied to metal-nitride-oxide-silicon (MNOS) structures. The technique consists of cooling the device to low temperatures and biasing it into the deep-depletion mode. The temperature of the device is then raised at a constant rate and the resulting I_g-T characteristic exhibits a pronounced wide peak. The energy level of the traps involved in the generation process was obtained from the slope of the log_eI_g - 1/T plot of the leading edge of the I_g-T characteristic curve, and is found to be 0·55 eV.A cross-check on the trap levels involved in the generation process was made by performing the experiment at two heating rates, β₁ and β₂. From a knowledge of the corresponding temperatures at which the maxima of the two peaks in the I_g-T characteristics occur, the energy level of the traps was found to be 0·54 eV. Furthermore, having obtained the trap level, the so-called carrier lifetime, τ, was found to be approximately 4μ sec.Experiments are described which provide convincing evidence that the generation of electron-hole pairs occurs in the depletion-layer of the silicon rather than at the silicon-silicon interface.     

Compositional dependence of work function and Fermi level position of the HfNx/SiO2 system

In situ Kelvin Probe (KP) measurements performed on HfN_x showed an increase of the vacuum work function as a function of N content from a value of 3.9 eV (silicon conduction band edge) for pure Hf to a value of 5 eV (silicon valence band edge) for x ～ 2. In contrast, capacitance–voltage (C–V) measurements showed that the effective work function increased only until x < 1 and saturated around a value of 4.6 eV (silicon midgap). This behavior is attributed to Fermi level pinning, which is probably due to oxidation of the HfN_x during the reactive sputtering deposition step.     

钒受主能级在n型4H-SiC中的深能级瞬态傅里叶谱和光致发光

借助深能级瞬态傅里叶谱研究了钒离子注入在SiC中引入的深能级陷阱.掺人的钒在4H-SiC中形成两个深受主能级,分别位于导带下0.81和1.02eVt处,其电子俘获截面分别为7.0 × 10-16和6.0×10-16cm2.对钒离子注入4H-SiC样品进行低温光致发光测量,同样发现两个电子陷阱,分别位于导带下0.80和1.6eV处.结果表明,在n型4H-SiC掺入杂质钒可以同时形成两个深的钒受主能级,分别位于导带下0.8±0.01和1.1±0.08eV处.     

Deep centers in neutron-transmutation-doped gallium arsenide

Three electron traps at 0.21, 0.27 and 0.68 eV below the conduction band edge and a hole trap at around 0.11 eV above the valence band edge have been observed in neutron-transmutation-doped liquid-phase-epitaxial GaAs. All four levels are undetectable after a heat treatment at 600°C for 5 min.     

Effect of Thermal Annealing on the Characteristics of Phosphorus-Implanted ZnO Crystals

A P-doped ZnO surface layer on undoped ZnO wafers was prepared by phosphorus (P) ion implantation. Hall effect measurement revealed p-type conduction in such layers annealed at 800°C. This indicates that acceptor levels are present in P-doped ZnO, even though the ZnO is still n-type. Micro-Raman scattering in ?z(xy)z geometry was conducted on P-implanted ZnO. The E ₂ ^high mode shift observed toward the high-energy region was related to compressive stress as a result of P-ion implantation. This compressive stress led to the appearance of an A ₁(LO) peak, which is an inactive mode. This A ₁(LO) peak relaxed during thermal annealing in ambient oxygen at temperatures higher than 700°C. The P2p_3/2 peak observed at 135.6 eV by x-ray photoelectron spectroscopy is associated with chemical bond formation leading to 2(P₂O₅) molecules. This indicates that implanted P ions substituted Zn sites in the ZnO layer. In photoluminescence spectroscopy, the P-related peaks observed at energies ranging between 3.1 and 3.5 eV originated from (A⁰, X) emission, because of P_Zn-2V_Zn complexes acting as shallow acceptors. The acceptor level was observed to be 126.9 meV above the valence band edge. Observation of this P-related emission indicates that ion implantation results in acceptor levels in the P-doped ZnO layer. This suggests that the P₂O₅ bonds are responsible for the p-type activity of P-implanted ZnO.     

Photoluminescence and raman studies of high quality CdTe:I Epilayers

Low-temperature photoluminescence (PL) studies of iodine-doped CdTe epilayers have been performed. A compensating acceptor center which gives rise to deep-level PL emission at 1.491 eV is identified. From selective excitation PL studies, we assign this 1.491 eV line to the recombination of an associate donor-acceptor close pair, consisting of nearest neighbor substitutional sodium and iodine atoms (Na_Cd-I_Te). This neutral defect complex has a localized mode of 36.5 meV, which is much larger than the bulk CdTe lattice mode of 21.3 meV. The electronic energy level associated with this defect is 115 meV below the conduction band. Also, we use a combination of selective excitation PL and Raman spectroscopies to determine the ionization energy of the isolated shallow iodine donor (I_Te) in CdTe. We find that the donor binding energy of this anion-site hydrogenic donor is 15.0 (±0.2) meV.     

Electronic properties of boron in p-type bulk 6H-SiC

The electronic properties of boron in bulk 6H-SiC have been studied by temperature dependent Hall effect, thermal admittance spectroscopy, and optical absorption. A single acceptor level located between 0.27 and 0.35 eV above the valence band is associated with boron on a silicon lattice site. The deep nature of this acceptor level prevents complete thermal activation of the level at room temperature and thus carrier concentration measurements at this temperature will not give the total boron concentration. A spread in the measured activation energy for boron is reported. Measurement of optical absorption is suggested as a nondestructive measure of boron concentration. No evidence for the D-center was observed in this material.     

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.     

Determination of deformation potential constants for <Emphasis Type="Italic">n</Emphasis>-and <Emphasis Type="Italic">p</Emphasis>-Si from the concentration anharmonicity

The contribution of charge carriers to the fourth-order modulus of elasticity β for n-and p-type silicon under uniaxial tension along the [110] direction was analyzed in the approximation of small strains. The effect of concentration on β was measured using spontaneous excitation of Lamb waves in bent plates with different doping levels. Experimental curves were used to determine the deformation potential constants of the conduction band Ξ_u=7±1 eV and the averaged value of the deformation potential of the valence band \(\sqrt[4]{{\left\langle {\Phi ^4 } \right\rangle }} = 5.6 \pm 0.8eV\) at room temperature.     

Photoluminescence identification of the C and Be acceptor levels in InP

Low dose (5x10⁹-5x10¹¹ cm⁻²) ion implantations of several ions including C, Be, Mg, and Mn have been performed into high purity epitaxial and bulk InP samples. A comparison of the low temperature (1.7-20 K) photoluminescence spectra of these deliberately doped samples was made to similar spectra of undoped high purity InP grown by LPE, PH₃-VPE, and LEC techniques in order to identify the residual acceptors in the undoped samples. Ionization energies obtained for the C, Be, and Mg acceptors (assuming E_g=1.4237 eV) were 44.6 ± 0.3, 41.3 ± 0.3, and 41.0 ± 0.3 me_gV, respectively. These valu were compared to the ionization energy of the dominant residual acceptor in LPE InP, which also occurs in LEC, polycrystalline, and PH₃-VPE material. This acceptor level was first reported in LPE InP by Hesset al. in 1974, who denoted it A₁; it has widely been assumed to be C. The value we measure for the ionization energy of A₁, which is 41.2 ± 0.3 meV, however, matches that of Mg and Be andnot C. We conclude that C is almost never present as a residual acceptor in undoped InP, and that the residual level in LPE and other material is Mg, or possibly Be. Similar measurements on Si and Sn doped samples showed no evidence of any Si or Sn acceptor level. The Mn acceptor peak was observed to occur at 1.19 eV.