Te vapor pressure dependence of the pn junction properties of PbTe liquid phase epitaxial layers

The pn junction characteristics of the PbTe epitaxial layers grown on PbTe substrates are investigated. Both the substrate crystals and the epitaxial layers are grown under controll Te vapor pressures. The ideality factors n of pn junctions decrease close to 1 in the temperature region from 40K to about 120K, but then increase with increasing temperature. The increase of n is more pronounced for higher Te vapor pressure. As a possible origin of the recombination current, deep levels with E_d=0.09 eV are found from Hall measurements for pn junctions grown under higher Te vapor pressure.     

放射状双pn结抑制片上电感衬底损耗

使用标准CMOS工艺,在放射状的n阱上面扩散p+,使垂直和水平方向形成双pn结,将此结放在电感的底部用来抑制衬底损耗.提出并实验证明了该结构形成的高阻区厚度不是垂直pn结耗尽层的厚度,而是最低层的pn结的深度.首次通过接地的p+扩散层屏蔽电感到衬底电场,水平和垂直pn结耗尽层厚度随着pn结反向偏压升高改变衬底有效的高阻区厚度,电感品质因数跟随高阻区厚度升降,有效地证明了pn结衬底隔离可以降低电感的衬底电流造成的损耗.     

放射状双pn结抑制片上电感衬底损耗

使用标准CMOS工艺,在放射状的n阱上面扩散p＋,使垂直和水平方向形成双pn结,将此结放在电感的底部用来抑制衬底损耗．提出并实验证明了该结构形成的高阻区厚度不是垂直pn结耗尽层的厚度,而是最低层的pn结的深度．首次通过接地的p＋扩散层屏蔽电感到衬底电场,水平和垂直pn结耗尽层厚度随着pn结反向偏压升高改变衬底有效的高阻区厚度,电感品质因数跟随高阻区厚度升降,有效地证明了pn结衬底隔离可以降低电感的衬底电流造成的损耗．     

Photoionization cross-sections and energy levels of gold,iron, platinum,silver, and titanium in silicon

The photoionization cross-sections of various deep impurities of interest in solar-grade silicon for photovoltaic cells, and the corresponding energy levels, have been determined by steady state photo-induced currents in pn junctions or Schottky barrier junctions irradiated simultaneously with two wavelengths of light. Light of about half the band-gap energy controls the occupancy of the deep impurity level and the spectral dependence of the photocurrent on a higher photon energy light source then provides, via the Lucovsky model, the photo-cross-section and the impurity energy level. The results obtained for Au and Pt in Si are in agreement with those of Braun and Grimmeiss and the energy levels for Fe, Ti, and Ag obtained optically are in agreement with those obtained by other methods.     

Recombination current measurements in the space charge region of MOS field-induced pn junctions

Electrically active defects in the device region are routinely monitored by CV measurements of reverse-biased field-induced (FI) pn junctions in MOS structures. While useful, this approach is sensitive only to near mid gap defects. Here, we demonstrate a method for interrogation of forward-biased FI pn junctions, which can reveal defect levels over a significantly wider region of the band gap. The method proposed is based on a simultaneous measurement of the gate current and the high frequency gate capacitance in non-equilibrium non-steady state in response to a linear gate voltage ramp which drives the MOS capacitor from inversion equilibrium towards accumulation. This recombination-sensitive technique enables a self-consistent determination of the forward current–voltage characteristic of the FI pn junction. It makes a wider range of important impurities, especially metallic contaminants, accessible to detection by MOS CV approaches. Since the approach satisfies the low-injection condition, the results can be directly related to the properties of the defect centres, thus facilitating defect identification and control.     

Electroluminescence and lasing properties of highly Bi-doped PbTe epitaxial layers grown by temperature difference method under controlled vapor pressure

Electroluminescence (EL) from PbTe pn homojunctions with a highly Bi-doped n-type emission layer with a concentration of N_Bi > 10¹⁹ cm⁻³, grown by the temperature difference method (TDM) under controlled-Te vapor pressure has shown a positive shift of the peak-photon energy, which coincides with the model that Bi atoms act as both donors and acceptors, and they make the nearest lattice-site or very close donor-acceptor (DA) pairs. Broad-contact pn junctions with highly Bi-doped layers easily cause laser emission compared to the difficulty in the lasing operation of undoped pn junctions, which suggests that the nearest lattice-site Bi-Bi DA pairs act as strong radiative centers in PbTe.     

Hydrogen Induced Yellow Luminescence in GaN Grown by Halide Vapor Phase Epitaxy

Strong yellow luminescence (YL) was found in GaN grown by the halide vapor phase epitaxy technique, using an NH₃-HCl-GaCl-N₂-H₂ growth chemistry. The low-temperature (less than 100K) thermal activation energy of the yellow luminescence was determined to be ∼18 meV, which indicates that a shallow donor, rather than a ‘shallow’ acceptor, was involved in observed radiative transition. The temperature dependence of the YL peak energy and the shape of the YL band imply that there are multiple recombination channels involved in the YL band. The ratio of integrated intensity of yellow-to-bandedge luminescence decreased with an increase of HCl (and hence GaCl and growth rate) in the growth ambient.     

The effects of Zn-vapor or Te-vapor heat treatment on the luminescence of ZnTe

We report cathodoluminescence measurements which show the effects of Zn-vapor or Te-vapor heat tretments on the edge emission and deep-center luminescence of vapor-phase-grown ZnTe. Prior to heat treatment, the 80 K luminescence of our as-grown material showed strong edge emission near 2.36 eV and weaker deep-center luminescence bands near 1.87 and 1.59 eV. The Te-vapor heat treatments induced a new luminescence band near 2.08 eV. The 1.59 eV band was enhanced by heat treatment in Te vapor and weakened by heat treatment in Zn vapor; this supports our earlier attribution of this band to a V_zn-related complex. In contrast, the initially weak red band near 1.87 eV was strongly enhanced by heat treatment, whether in either Zn vapor or Te vapor, followed by more rapid cooling than accorded the as-grown crystal. We thus conclude that the red band does not originate from a native-defect-related complex. The red luminescence is efficient and dominates the ZnTe spectrum from liquid nitrogen to room temperature. The electron-beam-current dependence, temperature dependence, and frequency-domain kinetics of the red band are reported following both Zn-vapor and Tevapor heat treatment. The red luminescence is attributed to recombination at isoelectronic 0 centers, the 0 being redistributed from precipitates to Te sublattice sites by the heat treatment and subsequent rapid cooling. This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract #DE-AC04-76DP00789.     

Elementary blue-emission bands in the luminescence spectrum of undoped gallium nitride films

Inhomogeneous broadening of the blue-emission band in the luminescence spectrum of nominally undoped gallium nitride films grown on substrates of sapphire with orientation (0001) and silicon with orientation (001) using chemical vapor deposition is observed. Studies of the emission spectra under different conditions of excitation of GaN films made it possible to detect three elementary bands with peaks at 2.65, 2.84, and 3.01 eV in the blue region of luminescence of these films at room temperature. Assumptions are made about the types of intrinsic and impurity defects involved in the formation of various centers in GaN as sources of blue emission.     

ZnO/SiC/Si(111)异质外延

使用SiC作为过渡层,采用自行设计建造的连通式双反应室高温MOCVD系统很好地克服了ZnO和SiC生长时的交叉污染问题,在Si基片上外延出高质量的ZnO薄膜.测量了样品的XRD和摇摆曲线,以及室温下的PL谱.实验结果表明,SiC过渡层的引入大大提高了ZnO薄膜的质量和发光性能,并有望实现在Si上制备ZnO单晶薄膜.     

Compositional dependence of cation impurity gettering in Hg1−xCdxTe

Cation impurity gettering in Hg_1−xCd_xTe is described in the context of process models which include the interactions of the impurities and the dominant native point defects. Experimental results are presented using secondary ion mass spectroscopy (SIMS) profiles of Au redistribution in Hg_1−xCd_xTe (x = 0.2,0.3,0.4) following Hg anneals and ion mills, which are processes known to inject excess Hg interstitials. In either process, the IB impurity distributes preferentially to high vacancy regions. The junction depth of the low to high impurity transition is determined by SIMS. For Hg-rich anneals of Au-doped high vacancy concentration material, the impurity junction behavior with respect to anneal time and temperature is compared to that expected for type converted electrical junctions in vacancy-only material. For milled Au-doped Hg_0.7Cd_0.3Te with a high vacancy concentration, the impurity junction depths are approximately proportional to the amount of material removed, as was the case with x = 0.2 material. Hg anneal type-conversion rates are found to have a strong compositional dependence which compares favorably with the strong self-diffusion coefficient dependence on x-value. In contrast, the mill conversion rate has a weak x-value dependence. Effects of trace vs dominant Au levels compared to the background vacancy concentration are quantified. True decoration of intrinsic defect processes requires Au <<[Cation Vacancies].     

Luminescence of stepped quantum wells in GaAs/GaAlAs and InGaAs/GaAs/GaAlAs structures

Luminescence spectra of doped and undoped GaAs/GaAlAs and InGaAs/GaAs/GaAlAs structures containing several tens of stepped quantum wells (QW) are investigated. The emission bands related to free and bound excitons and impurity states are observed in QW spectra. The luminescence excitation spectra indicate that the relaxation of free excitons to the e1hh1 state proceeds via the exciton mechanism, whereas an independent relaxation of electrons and holes is specific to bound excitons and impurity states. The energy levels for electrons and holes in stepped QWs, calculated in terms of Kane’s model, are compared with the data obtained from the luminescence excitation spectra. The analysis of the relative intensities of emission bands related to e1hh1 excitons and exciton states of higher energy shows that, as the optical excitation intensity increases, the e1hh1 transition is more readily saturated at higher temperature, because the lifetime of excitons increases. Under stronger excitation, the emission band of electron-hole plasma arises and increases in intensity superlinearly. At an excitation level of ～10⁵ W/cm², excitons are screened and the plasma emission band dominates in the QW emission. Nonequilibrium luminescence spectra obtained in a picosecond excitation and recording mode show that the e1hh1 and e2hh2 radiative transitions are 100% polarized in the plane of QWs.     

Analysis of defect related optical transitions in biased AlGaN/GaN heterostructures

The optical transitions in AlGaN/GaN heterostructures that are grown by metalorganic chemical vapor deposition (MOCVD) have been investigated in detail by using Hall and room temperature (RT) photoluminescence (PL) measurements. The Hall measurements show that there is two-dimensional electron gas (2DEG) conduction at the AlGaN/GaN heterointerface. PL measurements show that in addition to the characteristic near-band edge (BE) transition, there are blue (BL) and yellow luminescence (YL) bands, free-exciton transition (FE), and a neighboring emission band (NEB). To analyze these transitions in detail, the PL measurements were taken under bias where the applied electric field changed from 0 to 50 V/cm. Due to the applied electric field, band bending occurs and NEB separates into two different peaks as an ultraviolet luminescence (UVL) and Y₄ band. Among these bands, only the yellow band is unaffected with the applied electric field. The luminescence intensity change of these bands with an electric field is investigated in detail. As a result, the most probable candidate of the intensity decrease with an increasing electric field is the reduction in the radiative lifetime.     

Specific features of the metal-insulator conductivity transition in narrow-gap semiconductors of the MgAgAs structure type

The role of the impurity acceptor band in the conductivity of the doped and compensated ZrNiSn semiconductor is assessed. A reconstruction model of the impurity band as a result of doping the semiconductor with acceptor impurities is suggested. The electronic structure of the Zr_1?x Sc_xNiSn alloy is calculated. Oscillations of the magnetic susceptibility in the region of the metal-insulator transition (related to the Anderson transition) as the Zr_1?x Sc_xNiSn composition is varied are observed for the first time. These oscillations are believed to be a manifestation of the Coulomb gap in the impurity band as the levels of doping and compensation of the semiconductor are varied.     

Electronic structure of cubic silicon carbide with substitutional 3<Emphasis Type="Italic">d</Emphasis> impurities at Si and C sites

The full-potential linear muffin-tin orbital method is used to calculate the electronic structure and cohesive energies for cubic silicon carbide doped with transition 3d metal impurities (Me=Ti, V, Cr, Mn, Fe, Co, Ni), substituting Si or C at the corresponding sublattice of the atomic matrix. It is established that all 3d impurities mainly occupy silicon sites. For the Ti → Si substitution, dopant impurity levels are located in the conduction band of SiC, whereas doping silicon carbide with other 3d impurities gives rise to additional donor or acceptor levels in the band gap. For 3C-SiC the effect of impurities on the lattice parameter (with the substitutions Me → Si) and on the impurity local magnetic moments (with the substitutions Me → Si, C) is studied.     

Electron levels and luminescence of dislocation networks formed by the hydrophilic bonding of silicon wafers

Local energy levels produced by dislocations at the interface between bonded n- and p-Si wafers are studied by deep level transient spectroscopy and by a new technique for the detection of impurity luminescence, induced by the occupation of electron states upon the application of electric pulses (the pulsed trap-refilling-enhanced luminescence technique). It is established that only the shallow levels of the dislocation network, with activation energies of about 0.1 eV, are responsible for the D1 dislocation-related luminescence band in both n- and p-type samples. The occupation of deep levels has no effect on the D1-band intensity. A model of coupled neutral trapping centers for charge carriers is proposed. In this model, the difference between the energy position of the D1 band (0.8 eV) and the corresponding interlevel energy spacing (0.97 eV) is attributed to the Coulomb interaction between charge carriers trapped at the levels.     

非刻意掺杂4H-SiC同质外延中的深能级缺陷

Unintentionally doped 4H-SiC homoepitaxial layers grown by hot-wall chemical vapor deposition （HWCVD） have been studied using photoluminescence （PL） technique in the temperature range of 10 to 240 K. A broadband green luminescence has been observed. Vacancies of carbon （Vc） are revealed by electron spin resonance （ESR） technique at 110 K. The results strongly suggest that the green band luminescence, as shallow donor-deep accepter emission, is attributed to the vacancies of C and the extended defects. The broadband green luminescence spectrum can be fitted by the two Gauss-type spectra using nonlinear optimization technique. It shows that the broad-band green luminescence originates from the combination of two independent radiative transitions. The centers of two energy levels are located 2.378 and 2.130 eV below the conduction band, respectively, and the ends of two energy levels are expanded and superimposed each other.     

Deep level defects in unintentionally doped 4H-SiC homoepitaxial layer

Unintentionally doped 4H-SiC homoepitaxial layers grown by hot-wall chemical vapor deposition (HWCVD) have been studied using photoluminescence (PL) technique in the temperature range of 10 to 240 K. A broadband green luminescence has been observed. Vacancies of carbon (Vc) are revealed by electron spin resonance (ESR) technique at 110 K. The results strongly suggest that the green band luminescence, as shallow donor-deep accepter emission, is attributed to the vacancies of C and the extended defects. The broadband green luminescence spectrum can be fitted by the two Gauss-type spectra using nonlinear optimization technique. It shows that the broad-band green luminescence originates from the combination of two independent radiative transitions. The centers of two energy levels are located 2.378 and 2.130 eV below the conduction band, respectively, and the ends of two energy levels are expanded and superimposed each other.     

Luminescence and electrical properties of MgxZn1-xTe alloys

The luminescence and transport properties of high-quality undoped and phosphorus-doped Zn1-xMgxTe alloys (x ≤ 0.50) have been investigated. At 4.2 and 300 K, the photoluminescence of unintentionally doped crystals is dominated by near-band-edge recombination mechanisms. In phosphorus-doped samples, the luminescence spectra exhibit free-bound transitions involving shallow acceptor centers (phosphorus in tellurium sites). Whenxand/orTincreases, a broad luminescence band also appears at lower energy (1.7-1.9 eV) which decreases the near-band-edge luminescence efficiency. This low-energy band could be due to phosphorus atoms occupying other sites in the lattice (metal sites, for example) and then acting like deep recombination centers. Such a behavior could also explain the electrical properties of phosphorus-doped crystals. The introduction of phosphorus leads to an increase of the free hole concentration p as compared to undoped crystals but all phosphorus atoms do not behave as shallow acceptors; an increasing fraction of these atoms would act like donors in sites other than the tellurium sites as x increases. In undoped materials, p decreases drastically when we add more magnesium and the hole mobility remains approximately constant. We think that this effect is due to compensation by residual donor impurities. On these undoped samples, light-emitting diodes (LED's) have been successfully obtained for the first time. Their quantum efficiency is reasonable if we take into account the low carrier concentration of the material. The emission peak position is 5390 Å for Zn0.9Mg0.1Te instead of 5550 Å for undoped ZnTe.     

Effects of defect,carrier concentration and annealing process on the photoluminescence of silicon pn diodes

Silicon pn diodes were fabricated by ion implantation of B and P ions with different doses and subsequent annealing processes. Room temperature photoluminescence (PL) were investigated and the factors affecting the PL intensity were analyzed. Results show that both kinds of pn diodes have PL peak centered at about 1140 nm. Dislocation loops resulted from ion implantation and annealing process may enhance the light emission of silicon pn diode due to its band quantum confinement effect to carriers. The luminescence intensity depends on the carrier concentrations in the implantation region. It should be controlled at the range of 1–6×10¹⁶ cm⁻³. Moreover, the PL intensities of pn diodes with furnace annealing (FA) are higher than those with rapid thermal annealing, and the annealing temperature range for FA is 900–1100 °C.