Study of deep level defect behavior in undoped n-InP (1 0 0) after rapid thermal annealing

The effects of rapid thermal annealing on deep level defects in the undoped n-type InP with Ru as Schottky contact metal have been characterized using deep level transient spectroscopy (DLTS). It is observed that the as-deposited sample exhibit two deep levels with activation energies of 0.66 and 0.89 eV. For the samples annealed at 300 °C and 400 °C, a deep level is identified with activation energies 0.89 and 0.70 eV, respectively below the conduction band. When the sample is annealed at 500 °C, three deep levels are observed with activation energies 0.25, 0.32 and 0.66 eV. Annealing of the sample at 300 °C, orders the lattice of as-grown material by suppressing the defect 0.66 eV (A1) which is found in the as-deposited sample. The trap concentration of the 0.89 eV deep levels is found to be increased with annealing temperature. The deep level 0.32 eV may be due to the lattice defect by thermal damage during rapid thermal annealing process such as vacancies, interstitials and its complexes, indicating the damage of the sample after annealing at 500 °C. The defects observed in all the samples are possibly due to the creation of phosphorous vacancy or phosphorous antisite.     

LPE and VPE In1-xGaxAsyP1-y/InP: Transport properties, defects, and device considerations

The electrical properties of In1-xGaxAsyP1-yalloys lattice matched to InP, grown by liquid-phase and vapor-phase epitaxial techniques, have been determined by various measurements. Several electron and hole traps, with activation energies varying from 0.26 to 0.82 eV, have been identified by transient capacitance and photocapacitance measurements and their density and capture cross section have been measured. The 0.82 electron trap has emission and capture properties identical to the dominant 0.83 eV electron trap present in bulk and VPE GaAs. Hall measurements were made on the alloys in the temperature range of 20-600 K. Analysis of the mobility data has yielded the values of several transport parameters including the alloy scattering potentialDelta Uas a function of composition. The maximum value ofDelta U simeq 0.8eV corresponding to the bandgapE_{g} simeq 0.95eV. Photo-Hall measurements at low temperatures show the presence of donor- and acceptor-like defects in the LPE and VPE alloys, respectively. These centers exhibit persistent photoconductivity at low temperatures and have a high barrier energy (∼0.2 eV) associated with electron capture. Defects, which are possibly located in the interconduction-valley region, have been identified from analysis of Hall data forT > 400K. The strong temperature dependence of the threshold current in injection lasers and the large leakage currents near breakdown in avalanche photodiodes have been discussed in the fight of the defects identified in the present investigation.     

Deep level defects in Au/ZnSe Schottky diodes

Properties of deep level defects in heteroepitaxially grown ZnSe have been investigated using transient capacitance spectroscopy. A total of five electron traps were observed with activation energies of 0.33, 0.35, 0.42, 0.71 and 0.86 eV in Au/ZnSe Schottky diodes. Trap concentrations ranged from 1012 to 1014 cm?3.     

Hole traps in n-type Ga1?xAlxAs grown by organometallic vapour phase epitaxy

Minority carrier traps in n-type Ga1?xAlxAs (x = 0.25 and 0.30) grown by the organometallic vapour phase epitaxy process have been investigated by minority carrier transient spectroscopy (MCTS). Hole traps with thermal activation energies of Ev + 0.35 and 0.48 eV and a deeper centre have been observed in GaAs and at Ev + 0.20, 0.26, 0.44 and 0.78 in GaAlAs. The electron and hole capture cross-sections of these centres have also been measured.     

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.     

A detailed investigation of the D-X center and other trap levels in GaAs-AlxGa1-xAs modulation-doped heterostructures grown by molecular-beam epitaxy

We have re-examined the results and analysis of capacitance transient spectroscopy measurements made on modulation-doped heterostructures suitable for the fabrication of field-effect transistors. It is seen that conventional analysis of data can lead to erroneous results and a new model, which includes the contribution of the capacitance at the heterointerface, is presented. Most of the observed anomalous behavior related to trap emission can now be explained. Six main electron traps are present in single-layer AlxGa1-xAs, grown by molecular-beam epitaxy, and in device-quality GaAs-AlxGa1-xmodulation-doped heterostructures. These range in energy from 0.40 to 0.91 eV in thermal ionization energy. The well known D-X center in Si-doped AlxGal-xAs layers is composed of two closely spaced levels, DX1 and DX2, with ionization energies of 0.48 and 0.52 eV, respectively. At very low Si,doping levels, only DX2 is dominant, but at doping levels > 10¹⁸cm^-3, both DX1 and DX2 become comparable in concentration. The optical ionization properties of these levels were also measured and it is seen that the optical lineshapes differ markedly for the two centers. The peak photoionization cross sections occur at spectral energies of 1.25 and 1.38 eV for DX1 and DX2, respectively. The nature and symmetry of the centers have been studied by measurements on layers of different orientations.     

Pb(Mg1/3Nb2/3)O3-0.3PbTiO3单晶紫外可见近红外光学性质

通过温度依赖的透射和反射光谱研究了在准同型相界附近的Pb(Mg_(1/3)Nb_(2/3))O_3-0.3PbTiO_3(PMN-0.3PT)单晶光学性质.这种禁带宽度随温度范围不同变化规律不同现象,揭示了PMN-PT单晶温度依赖的复杂相结构.禁带宽度Eg在303 K是3.25 e V,临界点Ea是3.93 e V,临界点Eb是4.65 e V,它们随着温度的上升而下降,在453 K禁带宽度Eg是3.05 eV,临界点Ea是3.57 eV,临界点Eb是4.56 eV.这三个跃迁能量Eg、Ea、Eb分别对应从O 2p到Ti d、Ni d、Pb 6p轨道跃迁.它们随温度上升而下降的变化规律可以用晶格热膨胀和电子声子相互作用理论来解释.通过Tauc-Lorentz色散模型拟合得到了303 K到453 K温度范围的Pb(Mg_(1/3)Nb_(2/3))O3-0.3PbTiO_3单晶光学常数及其随温度的变化规律,发现折射率n随着温度的升高而升高.     

Analyses of transient capacitance experiments for Au---GaAs Schottky barrier diodes in the presence of deep impurities and the interfacial layer

Transient capacitance experiments have been performed for Au-n-type GaAs Schottky barrier diodes between 285 and 316°K. The GaAs substrates are doped with oxygen and chromium, respectively. From the transient dark-capacitance and photocapacitance measurements, the thermal emission rate, the doping densities and the thermal activation energies of oxygen and chromium impurities are obtained at T = 300°K.     

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.     

Structural and Optical Properties of ZnO Nanotips Grown on GaN Using Metalorganic Chemical Vapor Deposition

ZnO nanotips are grown on epitaxial GaN/c-sapphire templates by metalorganic chemical vapor deposition. X-ray diffraction (XRD) studies indicate that the epitaxial relationship between ZnO nanotips and the GaN layer is (0002)ZnO||(0002)GaN and (101̄0)ZnO||(101̄0)GaN. Temperature-dependent photoluminescence (PL) spectra have been measured. Sharp free exciton and donor-bound exciton peaks are observed at 4.4 K with photon energies of 3.380 eV, 3.369 eV, and 3.364 eV, confirming high optical quality of ZnO nanotips. Free exciton emission dominates at temperatures above 50 K. The thermal dissociation of these bound excitons forms free excitons and neutral donors. The thermal activation energies of the bound excitons at 3.369 eV and 3.364 eV are 11 meV and 16 meV, respectively. Temperature-dependent free A exciton peak emission is fitted to the Varshni’s equation to study the variation of energy bandgap versus temperature.