Titanium in silicon as a deep level impurity

Titanium inserted in silicon by diffusion or during Czochralski ingot growth is electrically active to a concentration level of about 4 × 10¹⁴ cm^?3. Hall measurements after diffusion show conversion of lightly doped p type Si to n type due to a Ti donor level at E_C - 0.22 eV. In DLTS measurements of n⁺p structures this level shows as an electron (minority carrier) trap at E_C - 0.26 eV with an electron capture cross section of about 3 × 10^?15 cm² at 300°K. The DLTS curves also reveal a hole trap in the p type material. The e_p (300/T)² activation plot gives the level as E_V + 0.29 eV. The hole capture cross section is about 1.7 × 10^?17 cm² at 300°K and decreases with decreasing temperature and the corrected trap level becomes E_V = 0.26 eV. Ti in lightly doped (360 ohm-cm) n type material does not result in conversion to p type so this level is inferred also to be a donor.A Ti electrically active concentration of about 1.35 × 10¹³ cm^?3 in p type (N_A = 3.35 × 10¹⁵cm^?3) Si results in a minority carrier (electron) lifetime of 50 nsec at 300°K.     

Application of the MOSFET device structure in characterizing imperfection centers in indium-doped silicon

C.T. Sah has published a review article demonstrating the application of high-frequency small signal capacitance and current transients of a space charge layer. Application of such transients is a powerful technique in characterizing deep level imperfection center concentrations, energy levels, thermal and optical emission rates and thermal capture cross sections. The MOSFET device structure is particularly convenient for low temperature measurements of shallow levels where deionization occurs and the substrate becomes highly resistive, seriously limiting capacitance transient techniques. Examples are given by results on indium-doped silicon, such as employed in extrinsic IR detectors. The emission time constant of holes from the neutral indium center has been found to depend on the indium doping. Measurements on lightly doped samples yield a value for the emission rate, $\text{1}\text{e}{}_{\mathrm{p}}$, of 6.0 msec at 77°K and a thermal activation energy of 0.15 eV. Measurements on heavily doped samples yield values of $\text{1}\text{e}{}_{\mathrm{p}}$ of 20 μsec at 77°K and an activation energy of 0.117 eV. These results are consistent with the Poole-Frenkel effect describing field enhanced thermal emission of holes from the indium center. Measurements of the hole capture coefficient at 77°K yield values for c_p of 3.7 × 10^?7 cm³/sec. These measurements have been made on heavily doped samples. The capture coefficient measured is the zero field or quasi-equilibrium value. The temperature dependence of the hole capture coefficient has been found to be T^?4. Small transients in the thermal emission rate measurements have been observed. These transients have thermal activation energies of around 0.08 eV and are associated with the 0.11 eV level as reported by Hughes Research Labs after accounting for barrier lowering by the Poole-Frenkel effect.     

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.     

Schottky-barrier capacitance measurements for deep level impurity determination

The time dependence of a Schottky-barrier capacitance due to thermal excitation of trapping centres has been studied. An expression for the junction capacitance is derived which is not restricted to any special range of reverse bias nor to a special relation between shallow and deep impurity concentration. The concentration ratio of shallow to deep centres is calculated from the values of the capacitance at zero and infinite time. From a capacitance vs. time plot the trap emission rate for electrons e_n is obtained. Their energetic level within the forbidden band-gap is determined from the temperature dependence of e_n as well as from the capacitance-time variation. Experimental studies which do confirm the calculations were carried out on gold contacts on oxygen-doped n-type GaAs. Representative results of the investigated samples were: shallow donor density 3 × 10¹⁵ cm^?3, trap density 9·8 × 10¹⁵ cm^?3, electron emission rate 6 × 10^?2 sec^?1, energetic level 0·68 eV and capture cross section 7 × 10^?16 cm².     

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p⁺–p⁰–i–n⁰ homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p⁰ and n⁰ layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E _t ), capture cross sections (σ _p ), and concentrations (N _t ) are calculated from the Arrhenius dependences to be E _t = 845 meV, σ _p = 1.33 × 10^–12 cm², N _t = 3.80 × 10¹⁴ cm^–3 for InGaAs/GaAs and E _t = 848 meV, σ _p = 2.73 × 10^–12 cm², N _t = 2.40 × 10¹⁴ cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.     

Identification of Cu-related thermally stimulated current trap in undoped semi-insulating GaAs

In the thermally stimulated current spectra of semi-insulating GaAs, a unique trap T_a at 170K is sometimes observed. The activation energy and capture cross section of T_a are 0.43 eV and 3.7×10⁻¹⁵ cm², respectively. Based on a good correlation with the Cu-related photoluminescence emission at 1.36 eV and the Cu-related deep level transient spectroscopy hole traps HL4 and HB4, we argue that T_a is a Cu-related hole trap.     

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.     

Capture cross sections of the gold donor and acceptor states in n-type Czochralski silicon

The hole and electron capture cross sections of the gold donor and acceptor have been measured directly in n-type silicon. The samples have been grown by the Czochralski technique and have originated from several different suppliers. They have been diffused with gold so that N_T ? 0.1 (N_D-N_A). Measurements have been made on both Schottky diodes and diffused junctions and similar results obtained from all samples. The electron cross section of the acceptor level was found to be (0.85±0.2) × 10^?16cm² and the hole cross section of the donor (3.5±0.8) × 10^?15cm², both were essentially temperature independent. The hole cross section of the acceptor was (0.9±0.2) × 10^?14cm² at 300 K and showed a T^?1.3 temperature dependence. The electron cross section of the donor was (0.9±0.2) × 10^?15cm² at 180 K with a T^?2 dependence.     

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.     

Vacancies in Hg1−xCdxTe

Measurements have been performed of the carrier concentrations in vacancy-doped Hg_1−xCd_xTe with x=0.22, 0.29, 0.45, and 0.5. Anneals to establish the carrier concentrations were performed on both the mercury- and tellurium-rich sides of the phase field. When these results were added to earlier data for x=0.2 and 0.4, and assuming that all vacancies are doubly ionized, then vacancy concentrations for all values of x and anneal temperature can be represented by simple equations. On the mercury side of the phase field, the vacancy concentrations varied as 2.50×10²³(1−x) exp[−1.00/kT] for low concentrations, and as 3.97×10⁷(1−x)^1/3n _i ^2/3 exp[−0.33/kT] for high concentrations, where n_i is the intrinsic carrier concentration. On the tellurium rich side, the vacancy concentrations varied as 2.81 × 10²²(1−x) exp[−0.65/kT] for low concentrations and as 1.92×10⁷(1−x)^1/3n _i ^2/3 exp[−0.22/kT] for high concentrations.     

Effects of Illumination on Ar<Superscript>+</Superscript>-Implanted <Emphasis Type="Italic">n</Emphasis>-Type 6H-SiC Epitaxial Layers

Argon ions were implanted into n-type 6H-SiC epitaxial layers at 600°C. Postimplantation annealing was carried out at 1,600°C for 5 min in an Ar ambient. Four implantation-induced defect levels were observed at E_C-0.28 eV, E_C-0.34 eV, E_C-0.46 eV, and E_C-0.62 eV by deep level transient spectroscopy. The defect center at E_C-0.28 eV is correlated with ED₁/ED₂ and with ID₅. The defect at E_C-0.46 eV with a capture cross section of 7.8 × 10⁻¹⁶ cm² is correlated with E1/E2, while the defect at E_C-0.62 eV with a capture cross section of 2.6 × 10⁻¹⁴ cm² is correlated with Z1/Z2. Photo deep level transient spectroscopy was also used to study these defects. Upon illumination, the amplitudes of the deep level transient spectroscopy (DLTS) peaks increased considerably. Two emission components of Z1/Z2 were revealed: one fast and the other slow. The fast component could only be observed with a narrow rate window. In addition, a new defect was observed on the low-temperature side of the defect at E_C-0.28 eV when the sample was illuminated. [rl](Received ...; accepted ...)     

Hole capture at acceptors inp-type germanium

Hole capture data obtained by capacitance transient spectroscopy on eleven different acceptors in high-purity germanium are presented over the temperature range 8–160 K. Capture invariably proceeded faster than predicted by the cascade theory and did not follow theZ ³ T ^?3 dependence predicted by cascade theory, whereZ is the acceptor charge andT is the temperature. Instead it was found that capture followed the phenomenological relationship $$\frac{{N_\upsilon }}{{gp\tau _c }} = kT/h\{ \eta exp (---E_a /kT) \} $$ whereN _υ is the effective density of states at the valence band edge,g is the degeneracy of the ground state (four),p is the hole concentration,τ _c is the mean capture time for the acceptor,k is Boltzman’s constant, andh is Planck’s constant.η is a dimensionless efficiency factor and exp (—E _α /kT) is an activation term required to fit the data of some centers. The authors propose that transitions to the electronic ground state from band states or from bound excited states must be faster than previously considered.     

Influence of Isotropic Pressure on the Current–Voltage Characteristics of Surface-Barrier Diodes Sb–<Emphasis Type="Italic">p</Emphasis>-Si〈Mn〉–Au

The influence of hydrostatic pressure on the current–voltage characteristics of surface-barrier diode structures of the Sb–p-Si〈Mn〉–Au type are investigated. The potential-barrier height and the baric coefficient of its variation are found to be e?_δ = 0.75 eV and δ =–1.54 × 10^–11 eV/Pa, respectively.     

Impurity states in cobalt-doped silicon

Cobalt was diffused into p⁺ pn⁺ silicon structures at 900° and 1150°C for 2−4 hours followed by various quenching conditions. Four primary hole traps and two electron traps associated with cobalt in these devices were observed. The hole traps are labeled H1(E_v + 0.22 eV), H2(E_v + 0.29 eV), H3 (E_v + 0.40 eV) and H4(E_v + 0.45 eV) while the electron traps labeled E1 and E2 are located at E_c − 0.36 eV and E_c − 0.44 eV, respectively. The concentrations, thermal emission rates, and the capture cross sections for the majority carriers at these defects are reported. The behavior of these defects under heat treatment and the emergence of secondary defects, H5(E_v +0.22 eV) and H6 (E_v +0.34 eV), will be discussed.     

Sulphur doped silicon IR detectors

Experimental data on the electrical transport properties and photoconductive detector performance of sulphur doped silicon as a function of temperature are presented. Analysis of the data shows that the detector performance is determined by a donor level at 0.19 eV from the conduction band edge with an electron capture cross section of 2 × 10^?13 cm² and a peak photoionization cross section of 1 × 10^?16 cm². Photoconductivity has been observed at 95 K which may be associated with a centre 0.37 eV below the conduction band.     

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.     

Study of electrically active defects in n-GaN layer

Deep level defects in both p⁺/n junctions and n-type Schottky GaN diodes are studied using the Fourier transform deep level transient spectroscopy. An electron trap level was detected in the range of energies at E_c−E_t=0.23–0.27 eV with a capture cross-section of the order of 10⁻¹⁹–10⁻¹⁶ cm² for both the p⁺/n and n-type Schottky GaN diodes. For one set of p⁺/n diodes with a structure of Au/Pt/p⁺–GaN/n–GaN/n⁺–GaN/Ti/Al/Pd/Au and the n-type Schottky diodes, two other common electron traps are found at energy positions, E_c−E_t=0.53–0.56 eV and 0.79–0.82 eV. In addition, an electron trap level with energy position at E_c−E_t=1.07 eV and a capture cross-section of σ_n=1.6×10⁻¹³ cm² are detected for the n-type Schottky diodes. This trap level has not been previously reported in the literature. For the other set of p⁺/n diodes with a structure of Au/Ni/p⁺–GaN/n–GaN/n⁺–GaN/Ti/Al/Pd/Au, a prominent minority carrier (hole) trap level was also identified with an energy position at E_t−E_v=0.85 eV and a capture cross-section of σ_n=8.1×10⁻¹⁴ cm². The 0.56 eV electron trap level observed in n-type Schottky diode and the 0.23 eV electron trap level detected in the p⁺/n diode with Ni/Au contact are attributed to the extended defects based on the observation of logarithmic capture kinetics.     

Defects Study in Hg x Cd1−x Te Infrared Photodetectors by Deep Level Transient Spectroscopy

At high temperature, infra-red focal plane arrays are limited by their performance in operability, detectivity D ^* or noise equivalent temperature difference. Trap characterization and defect studies are necessary to better understand these limitations at high temperature. In this paper, we use deep level transient spectroscopy to study electrically active defects in mercury cadmium telluride n ⁺/p diodes. The material investigated has a cut-off frequency (λ _c) of 2.5 μm at 180 K and p doping performed with mercury vacancy. Trap energy signatures as well as capture cross-section measurements are detailed. A low temperature hole trap close to midgap is observed in the range 150–200 K with an activation energy around 0.18 ± 0.025 eV. A high temperature hole trap is also observed in the range 240–300 K with an activation energy of 0.68 ± 0.06 eV. A hole capture cross-section of 10^?19 cm² is obtained for both traps. The nature of the defects and their correlation with dark current are discussed.     

Characterization of the iron and nickel impurities in gaas0.6p0.4

Characterization of nickel and iron impurity centers in GaAs_0.6P_0.4 has been made using the technique of capacitance transients on reverse biased zinc-diffused p⁺n diodes. Both the nickel and iron levels have been identified by thermal hole emission having activation energies of 0.3eV and 0.58eV, respectively. Relative photoresponse measurements resulted in a threshold for optical hole emission of 0.3eV and 0.58eV, therefore, confirming the thermal hole emission measurements. Capture studies for nickel and iron centers indicated a relatively large capture cross-section and a strong electric field dependence. This work is supported by the National Science Foundation, Grant ENG76-80128.     

Transient and steady state space-charge-limited current in CdTe

The current response to pulsed and constant external bias is studied on wafers of semi-insulating CdTe crystals which are provided with contacts of aquadag. Space-charge-limited current (sclc) is observed. The magnitude of the large-signal turn-on transient current suggests that electrons are the injected carriers. The time constant of the current decay yields a value of the electron trapping time τ⁺ of ～ 10^?7 sec. Double pulse experiments provide the value of the detrapping time τ_D and its activation energy E_t = 0.65 eV. From these quantities, a trap concentration N_t = 0.85 × 10¹²cm^?3 and a trapping cross-section σ = 3.8 × 10^?13 are deduced. The results are compared with the d.c. characteristic of the devices and with data reported in the literature. Good agreement is obtained, indicating the usefulness of transient and d.c. sclc for characterizing semi-insulating materials and the injecting nature of the contacts.