DLTS investigation of GaP under hydrostatic pressure

Abstract

Deep Level Transient Spectroscopy (DLTS) was applied to nitrogen related deep electron trap 0.4 eV in green emitting diodes of GaP under hydrostatic pressure. The pressure coefficient of the level energy is determinated as equal -31 meV/kbar with respect to the valence band edge.     

InP-SiO2 metal-insulator-semiconductor structure parameters investigated with DLTS and other capacitance techniques

In this paper, we report the study of a n-type InP-SiO₂ Metal-Insulator-Semiconductor structure by means of Deep Level Transient Spectroscopy and two complementary techniques : Capacitance versus Voltage and Conductance versus Frequency measurements. We have observed two bulk traps probably related to impurities in the InP crystal. Majority carrier interface states have been studied : the three methods bring similar density profiles showing a minimum value about 10¹² eV^-1 cm^-2 in the energy range 0.4–0.7eV below the conduction band edge. Moreover, we have detected a “missing Phosphorus” interface level at 0.3 eV below the conduction band with a density about 4 x 10¹⁰ cm^-2.     

Deep level transient spectroscopy in Hg1−xCdxTe

We report the application of Deep Level Transient Spectroscopy (DLTS) in Hg_1-xCd_xTe, demonstrating for the first time the utilization of DLTS techniques in a narrow band-gap semiconductor, E_g < 0.40 eV. DLTS measurements performed on an n⁺-p diode with E_g (x=0.21, T=30 K) =0.096 eV have identified an electron trap with an energy of E_v + 0.043 eV and a hole trap at E_v + 0.035 eV. Measurements of trap densities, capture cross sections, and the close proximity of the electron and hole trap locations within the band-gap suggest that DLTS may be observing both the electron and hole capture at a single Shockley-Read recombination center. The trapping parameters measured by DLTS predict minority carrier lifetime versus temperature data to be comparable with the experimentally measured values.     

Deep level transient spectroscopy of hole traps in Zn-annealed ZnTe

Hole traps in Schottky barrier diodes of p-ZnTe that had previously been annealed in liquid Zn have been investigated using Deep Level Transient Spectroscopy (DLTS). Three traps have been investigated in 3etail and have activation energies of between E_v = 0.28 eV and E_v + 0.59 eV. All traps are assigned to acceptor defects because of their large capture cross sections for holes and one of these is tentatively assigned to a V_Zn native acceptor. From capacitance-temperature plots we deduce that Cu_Zn is the dominant shallow acceptor in as-grown material but after annealing the Cu_Zn concentration is reduced and a yet shallower acceptor, probably Li_Zn, predominates.     

DLTS studies of deep levels in semiconducting N-CdTe single crystals

Deep levels created by annealing of Al-doped n-CdTe single crystals have been studied by the Deep Level Transient Spectroscopy (DLTS) technique. Eight levels have been detected in the energy range from 0.04 to 0.07 eV below the conduction band edge. The thermal ionization energies and the capture cross sections for electrons in these levels have been obtained. The dependence of concentrations of the levels on the Cd vapor pressure during annealing and on the cooling process after annealing has been determined.     

Investigation of the effect of CdCl2 processing on vacuum deposited CdS/CdTe thin film solar cells by DLTS

Thin film CdS/CdTe solar cells have been prepared by conventional vacuum deposition technique. Deep level transient spectroscopy (DLTS), temperature and frequency dependent capacitance-voltage (C-V) measurements were utilised to investigate the performance limiting defect states in the CdTe layer subjected to the post deposition treatments such as CdCl₂-dipping and/or annealing in air. Five hole traps, all of which have been previously reported in the literature, were identified in as-grown CdTe at 0.19, 0.20, 0.22, 0.30 and 0.40 eV above the valence band. A single hole trap level has been evidenced at 0.45 eV after both post deposition heat and CdCl₂ treatments.     

Determination of deep electron traps in GaAs by time-resolved capacitance measurement

A useful technique of determining the energy levels and the spatial density distributions of multiple electron traps in semi-conductor has been developed using the time-resolved measurement of the Schottky barrier junction capacitance, and this technique has been applied to characterize the electron traps inn-GaAs. In the present technique, the energy levels are determined from single scan of temperature, and the density distributions are calculated from a set of capacitance-voltage relationships. Four traps which lay at 0.39, 0.73, 0.79, and 0.58 eV below the conduction band edge were observed in boat grown or vapor phase epitaxially grown crystals. Many layers which were obtained by a vapor phase epitaxial growth system with N₂ carrier gas were measured and it was found that almost all of them include the 0.73 eV and the 0.79 eV trap with the density between 1×10¹³ and 2×10¹⁵ cm⁻³.     

Improvement in the determination of accuracy of enthalpy of ionization from the isothermal deep level transient spectroscopy

In this paper we propose to use a combination of a modified isothermal Deep Level Transient Spectroscopy (IDLTS) method with optical excitation and a filtering method of multi-exponential decays for IDLTS signal represented by a nonexponential transient capacitance. Excellent agreement with published results is achieved using this method for the investigation of a hole trap response (HL4) interfering with other traps in Schottky barriers that were fabricated on an epitaxial GaAs layer grown by VPE on bulk N-GaAs.The authors express sincere thanks to I. Thurzo and F. Dubecký of the Slovak Academy of Sciences who provided samples for these experiments and for useful advice.     

注硅半绝缘GaAs的深能级

用深能级瞬态谱(DLTS)详细研究了硅离子注入Liquid-encapsulated Czochralski(缩写为LEC)半绝缘GaAs的深中心。结果表明,在注硅并经高温退火的有源区中观测到4个多子(电子)陷阱,E₀₁,E₀₂,E₀₃和E₀₄。它们的电子表观激活能分别为0.298,0.341,0.555和0.821eV。其中E₀₄与EL2有关,但不是EL2缺陷。E₀₄的电子 关键词：     

Electron traps in CdS single crystals obtained by admittance spectroscopy on the hetero- and Schottky junctions

The electron trap parameters in semiconducting CdS single crystals were obtained by admittance spectroscopy on its hetero- and Schottky junctions, and the trap depths obtained were 0.065, 0.09, 0.15 0.20, and 0.40 eV. The capture cross-section of the shallowest trap on the Cd-face of the crystals was about 10⁻¹⁹ cm², one order smaller than that of the bulk crystal. The resolving power of the employed method was about 50 meV to distinguish the two traps with different depths. The results of the computer simulation of this method suggested that the trap can be determined when the trap density is at least one order lower than the donor density. The calculated density of the each trap was 1×10¹⁵ cm⁻³ for the shallowest trap and 2×10¹⁶ cm⁻³ for the remaining traps, respectively.     

Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at E_v+0.128~eV, originates from the vacancy of Cd (V_Cd. The electron trap E1, found at E_c-0.178~eV, is considered to be correlated with the interstitial Cu_i⁼ in CdTe.     

n‐type conductivity in sublimation‐grown AlN bulk crystals

AlN crystals grown by physical vapour‐phase transport in the presence of a SiC doping source possess n‐type conductivity. The net donor concentration attains up to mid 10¹⁷ cm^–3. The investigation reveals shallow donors forming an impurity band and acceptor‐like electron traps at about 0.5 eV below the conduction band edge. Thermal electron emission from these traps is responsible for the observed n‐type conductivity. The shallow donors are suggested to be due to Si atoms on Al sites. The majority of them is assumed to be compensated by deep acceptors in the lower half of the band gap. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interstitial iron and iron-acceptor pairs in silicon

Deep levels in iron-dopedp-type silicon are investigated by means of Deep Level Transient Spectroscopy (DLTS) and the Hall effect. Pairs of Fe with the acceptors B, Al, and Ga are observed at 0.1, 0.19, and 0.24 eV above the valence band edgeE _v. For interstitial iron, (Fe _i ), a level energy ofE _v+0.39+-0.02 eV is obtained with DLTS after correction with a measured temperature dependence of the capture cross section. The Hall effect yieldsE _v+0.37 eV for Fe_i. The annealing behavior of levels related to Fe is investigated up to 160 °C. Iron participates in at least four different types of impurity states: Fe _i , Fe-acceptor pairs, precipitations (formed above 120 °C) and an additional electrically inactive state, which is formed at room temperature.     

Electron and hole traps in N-GaAs crystals

Deep traps were measured and their electronic and optical properties were determined by junction capacitance techniques in n-GaAs crystals grown by different methods. Four electron-traps and four hole-traps were detected. An electron trap was not observed in LPE wafers. A hole trap at 0.45 eV above the top of the valence band was detected in all wafers measured here.     

Space charge limited currents in high resistivity CdTe crystals

DC-measurements of SCLC of high resistivity Cl-compensated p-type crystals of CdTe have been performed in the temperature range of 230–300 K. The evaluation of voltage-current characteristics by means of a simple model with discrete trap levels led to activation energies of approx. 0·65 and 0·4 eV above the valence band and trap concentrations of the order 10¹¹ to 10¹² cm^–3.The authors thank Dr. P.Höschl for supplying the crystals and for fruitful discussions.     

Influence of deformation on the conductivity and photoconductivity of p-Type CdTe

Samples of p-type CdTe were subjected to deformation. Studies were performed of the influence of 60°-dislocations on the electrical conductivity, on the lifetime of minority carriers and on the relative change of the conductivity due to illumination. Dislocations were produced by bending the sample that was cut at suitable orientation. In this way, one obtained the 60°-dislocations, either of α- or β-type, according to the kind of bending involved. From the measurement of the temperature dependence of the conductivity it was ascertained that an increase in acceptor concentration occurs on the level with activation energy of 0.3 eV (identical to that of V^cd or a complex with V^cd), regardless of the type of dislocations. The concentration of acceptors on the level with activation energy 0.3 eV increases on increasing the dislocation density. The most probable explanation is that the deformation and, especially, annealinginduced migration of the dislocations produced give rise also to V^cd and/or V^Te (both types simultaneously). V^cd acts as an acceptor and V^Te as a donor. It follows that the increase in V^Te can not be established from this measurement. The lifetime of the minority carriers is almost unaffected by introducing the dislocations into the samples. From the temperature dependence of the relative change in conductivity due to illumination one can determine the activation energy of a dislocation level provided that one assumes the dislocations acting as recombination centers. Under this assumption one obtainsE _d =0.21–0.24 eV (for type α) andE _d =0.55–0.59 eV (for type β), measured from the top of the valence band.     

Charge transport mechanism in thin films of amorphous and ferroelectric Hf0.5Zr0.5O2

The charge transport mechanism in thin amorphous and ferroelectric Hf_0.5Zr_0.5O₂ films has been studied. It has been shown that the transport mechanism in studied materials does not depend on the crystal phase and is phonon-assisted tunneling between traps. The comparison of the experimental current–voltage characteristics of TiN/Hf_0.5Zr_0.5O₂/Pt structures with the calculated ones provides the trap parameters: thermal energy of 1.25 eV and the optical energy of 2.5 eV. The trap concentration has been estimated as ~10¹⁹–10²⁰ cm^–3.     

Investigation of the effects of gamma radiation on the electrical properties of dilute GaAs1−xNx layers grown by Molecular Beam Epitaxy

This work reports the effect of gamma (γ-) irradiation on dilute GaAsN with nitrogen concentrations ranging from 0.2 to 1.2% with post-irradiation stability using Current–Voltage (I–V) and Deep Level Transient Spectroscopy (DLTS) measurements in the temperature range from 10 K to 450 K. The I–V results indicate that the irradiation effect was more pronounced in the samples with nitrogen concentration of 0.4%. Additionally, the irradiated samples showed an ideality factor higher than the as-grown samples. On the other hand, for temperatures above 265 K the barrier height of the irradiated samples with 0.8% nitrogen is higher than the as-grown samples. The DLTS measurements revealed that after irradiation the number of traps either decreased remained constant, or new traps are created depending on the concentration of nitrogen. For samples with N = 0.2% – 0.4% the number of traps after irradiation decreased, whereas for samples with N = 0.8% − 1.2 % the number of traps remained the same. However, the properties of some traps such as capture cross-sections and density increased by about 2 orders of magnitude. The origin of the defects present before and after irradiation are discussed and correlated.     

Features of OSL and TL properties of anion-defective corundum crystals exposed to thermo-optical treatment

The results of systematic investigation of the mechanisms and role of phototransfer in TL and OSL processes in α-Al₂O_3−δ crystals under controlled filling of the main and deep traps depleted at 450 and 720 K, respectively, are presented.Optical depletion spectra of the main and deep traps were measured and compared. It was found that green light stimulation only depletes the main trap, while blue light depletes both the main and deep traps. Optical depletion of the deep trap results in phototransfer of charges that can be realized by 2 mechanisms: either through the main trap to recombination centers or directly to the latter. However, the dominant contribution to the OSL signal is provided by phototransfer through the main trap. It is also found that UV emission at 3.7 eV dominates over F-emission at 3.0 eV in the phototransferred TL spectrum. It is assumed that this UV emission is not related to the F⁺ centers.     

双异质结AlxGa1-xAs/GaAs发光管中与氧有关能级的测量

用DLTS和单次脉冲瞬态电容技术研究了液相外延生长的双异质结AlxGa1-xAs/GaAs发光管,掺Si的n-Al0.05Ga0.95As有源层中的深能级。着重分析了一个与氧有关的电子陷阱,其发射激活能为EC-ED=0.29eV。我们发现该电子陷阱随正向注入脉冲宽度tp的增加DLTS峰向低温移动,即在确定的温度下发射率随tp的增加而增加。用DLTS首次测得该能级的俘获瞬态谱,发现俘获峰随反向撤空脉冲宽度tR的增加向低温端移动,即在确定的温度下俘获率随tR的增加而增加,并且俘获激活能从△Eσ=0.28eV变化到0.26eV,用位形坐标图讨论了引起变化的原因。