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1.
In the paper, the comparative analysis of type-II InAs/GaSb SLs deposited on three types of GaSb buffers: homoepitaxial, metamorphic and one grown using the interfacial misfit (IMF) array technique has been presented. The buffer layers as well as superlattices were grown under nominally identical technological conditions. HRXRD investigations proved better crystal quality of the metamorphic material than the IMF-GaSb. FWHMRC were equal to 156 arcsec and 196 arcsec, respectively. The surface roughness of about 1?ML and 4?MLs was obtained using the atomic force microscope for 4.0?μm–metamorphic GaSb and 1.5?μm-IMF-GaSb layers, respectively. The etch pits density for both buffers was similar, 1–2?×?107?cm?2. Superlattice with 500 periods deposited on the homoepitaxial buffer was used as a reference of the best crystal quality. HRTEM images revealed straight InAs/GaSb interfaces with 1?ML thicknesses in this sample. The interfaces in SL deposited on IMF-GaSb buffer were undulated and smeared over 3?MLs. The use of the metamorphic buffer resulted in 1–2?ML straight InAs/GaSb interfaces. The main reason for this is the roughness of IMF-GaSb buffer with mounds on the surface. Based on the obtained results we have demonstrated the advantage of metamorphic approach over IMF growth mode in GaSb/GaAs material system. A two times thicker buffer could be the price worth paying for high quality structures, even when working in the production mode.  相似文献   

2.
The effects of bombardment of 250 keV argon ions in n-type GaSb at fluences 2×1015 and 5×1015 ions cm?2 were investigated by high-resolution X-ray diffraction (HRXRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). HRXRD studies revealed the presence of radiation-damaged layer (strained) peak in addition to the substrate peak. The variation in the lattice constant indicates the strain in the bombarded region. The out-of-plane (?) and in-plane strains (?|) determined from the profiles of several symmetric and asymmetric Bragg reflections, respectively, were found to change with the ion fluence. Simulations of XRD patterns using dynamical theory of X-ray scattering (single-layer model) for the damaged layer yielded good fits to the recorded profiles. FTIR transmission studies showed that the optical density (α·d) of GaSb bombarded with different fluences increases near the band edge with increase in ion fluence, indicating the increase in the defect concentration. The density of the defects in the samples bombarded with different fluences was in the range of 3.20×1021–3.80×1021 cm?3. The tailing energy estimated from the transmission spectra was found to change from 12.0 to 58.0 meV with increasing ion fluences, indicating the decrease of crystallinity at higher fluences. SEM micrographs showed the swelling of the bombarded surface of about 0.33 μm for the fluence of 2×1015 ions cm?2, which increased to 0.57 μm for the fluence of 5×1015 ions cm?2.  相似文献   

3.
王永宾  徐云  张宇  迂修  宋国峰  陈良惠 《中国物理 B》2011,20(6):67302-067302
This paper presents a theoretical study on the electrical and optical properties of mid-infrared type-II InAs/GaSb superlattices with different beryllium concentrations in the InAs layer of the active region. Dark current, resistance-area product, absorption coefficient and quantum efficiency characteristics are thoroughly examined. The superlattice is residually n-type and it becomes slightly p-type by varying beryllium-doping concentrations, which improves its electrical performances. The optical performances remain almost unaffected with relatively low p-doping levels and begin to deteriorate with increasing p-doping density. To make a compromise between the electrical and optical performances, the photodetector with a doping concentration of 3 × 1015 cm-3 in the active region is believed to have the best overall performances.  相似文献   

4.
Enhanced Hall mobility has been measured in Si doping superlattices with pipi or nini doping profiles grown by molecular beam epitaxy. Although the carrier concentration is large, in the range of 1018cm−3, the mobility of holes in the pipi doping superlattice has the temperature dependence such as that expressed in the T−2.2 law which is characteristic of high purity bulk crystals. The hole mobility is about twice that of high purity crystals, rising up to 40,000 cm2/V.s at about 30 K. In the case that p-type impurity concentration is comparable to n-type impurity concentration, no mobility enhancement is observed and the mobility is anomalously depressed. The mechanisms for drastical change in the mobility of doping superlattices have not yet been clarified.  相似文献   

5.
AlN with different thicknesses were grown as interlayers (ILs) between GaN and p-type Al0.15Ga0.85N/GaN superlattices (SLs) by metal organic vapor phase epitaxy (MOVPE). It was found that the edge-type threading dislocation density (TDD) increased gradually from the minimum of 2.5×109?cm?2 without AlN IL to the maximum of 1×1010?cm?2 at an AlN thickness of 20 nm, while the screw-type TDD remained almost unchanged due to the interface-related TD suppression and regeneration mechanism. We obtained that the edge-type dislocations acted as acceptors in p-type Al x Ga1?x N/GaN SLs, through the comparison of the edge-type TDD and hole concentration with different thicknesses of AlN IL. The Mg activation energy was significantly decreased from 153 to 70?meV with a?10-nm AlN IL, which was attributed to the strain modulation between AlGaN barrier and GaN well. The large activation efficiency, together with the TDs, led to the enhanced hole concentration. The variation trend of Hall mobility was also observed, which originated from the scattering at TDs.  相似文献   

6.
Gallium antimonide (GaSb) films were deposited onto fused silica and n-Si (100) substrates by coevaporating Ga and Sb from appropriate evaporation sources. The films were polycrystalline in nature. The size and the shape of the grains varied with the change in the substrate temperature during deposition. The average surface roughness of the films was estimated to be 10 nm. Grain boundary trap states varied between 2×1012 and 2.2×1012 cm?2 while barrier height at the grain boundaries varied between 0.09 eV and 0.10 eV for films deposited at higher temperatures. Stress in the films decreased for films deposited at higher temperatures. XPS studies indicated two strong peaks located at ~543 eV and ~1121 eV for Sb 3d3/2 and Ga 2p3/2 core-level spectra, respectively. The PL spectra measured at 300 K was dominated by a strong peak located ~0.55 eV followed by two low intensity peaks ~0.63 eV and 0.67 eV. A typical n-Si/GaSb photovoltaic cell fabricated here indicated V oc~311 mV and J~29.45 mA/cm2, the density of donors (N d)~3.87×1015 cm?3, built in potential (V bi)~0.48 V and carrier life time (τ)~28.5 ms. Impedance spectroscopy measurements indicated a dielectric relaxation time ~100 μs.  相似文献   

7.
The defect structure of AlGaN/GaN superlattices and GaN layers grown through vapor-phase epitaxy from organometallic compounds is investigated using x-ray diffraction analysis before and after implantation with erbium ions at an energy of 1 MeV and a dose of 3 × 1015 cm?2, as well as after annealing. For a superlattice with a total thickness larger than the implantation depth, the satellites of the superlattice region strained under the action of ions disappear in the x-ray diffraction pattern after annealing at temperatures higher than 900°C. This suggests that the radiation-induced defects responsible for the positive deformation in the layer are annealed at these temperatures. However, annealing even at a temperature of 1050°C does not lead to complete recovery of the initial state and the positive deformation in the remaining regions is caused by residual defects. An analysis of the x-ray diffraction patterns demonstrates that, in samples with thin superlattices located at the depth corresponding to maximum radiation damage, the periodic structure that disappears after implantation at a dose of 3 × 1015 cm?2 is not recovered even after annealing at a temperature of 1050°C. This inference is confirmed by the results of examinations with an electron microscope.  相似文献   

8.
Hall measurements are reported for undoped and Zn-doped vapor-grown single crystal GaN on (0001) Al2O3 layers with 298 K carrier concentrations (n-type) between 1·4×1017cm?3 and 9×1019 cm?3. Then n~1017 cm?3 crystals (undoped) have mobilities up to μ~440 cm2/V sec at 298 K. Their conduction behavior can be described by a two-donor model between 150 and 1225 K and by impurity band transport below 150 K. Crystals with n≥8×1018 cm?3 show metallic conduction with no appreciable variation in n or μ between 10 and 298 K.Results of mass spectrographic analyses indicate that the total level of impurities detected is too low to account for the observed electron concentration at the n~1019 cm?3 level, and suggest the presence of a high concentration of native donors in these crystals. No significant reduction in carrier concentration was achieved with Zn doping up to concentrations of ~1020 cm?3 under the growth conditions of the present work, and no evidence was found to indicate that high conductivity p-type behavior may be achieved in GaN. The influence of factors such as growth rate, crystalline perfection and vapor phase composition during growth on the properties of the layers is described.  相似文献   

9.
Molybdenum-doped cadmium oxide films were prepared by a spray pyrolysis technique at a substrate temperature of 300?°C. The effect of doping on structural, electrical and optical properties were studied. X-ray analysis shows that the undoped CdO films are preferentially oriented along the (111) crystallographic direction. Molybdenum doping concentration increases the films?? packing density and reorients the crystallites along the (200) plane. A?minimum resistivity of 4.68×10?4????cm with a maximum mobility of 75?cm2?V?1?s?1 is achieved when the CdO film is doped with 0.5?wt.% Mo. The band-gap value is found to increase with doping and reaches a maximum of 2.56?eV for 0.75?wt.% as compared to undoped films of 2.2?eV.  相似文献   

10.
Abstract

Hall coefficient (RH) and electrical resistivity measurements have been performed as a function of temperature (between 77 K and 300 K) and under hydrostatic pressures (up to 15 kbar) on a set of Se-doped GaSb samples with impurity concentrations in the range 8×1017 cm?3 - 1×1018 cm?3. With increasing pressure at 300 K, the electrons are strongly trapped into a resonant impurity level. The pressure induced occupation of this level leads to time-dependent effects at T<120 K. The activated thermal electron emission over a potential barrier E<sb>B = 300×30 meV gives clear evidence for a large lattice relaxation around the impurity centers characteristic for DX-like behavior.  相似文献   

11.
《Infrared physics》1990,30(1):27-32
We propose that nipi superlattice structures in InSb or InAs can be grown with modern techniques to achieve tunable and stable LWIR detectors with high performance. We examine key device and material considerations for the application of such nipi superlattices to LWIR detectors. It is shown that practical absorption coefficients (≈ 100 cm−1) can be achieved with high doping concentrations (≈ 1019 cm−3) achievable in these materials. In particular, recent delta doping techniques being developed in molecular beam epitaxy offer promise of higher doping concentrations, improved uniformity, and greater flexibility in tailoring the structures for optimum detector performance.  相似文献   

12.
The paper reports on the barrier mid-wave infrared InAs/InAsSb (xSb = 0.4) type-II superlattice detector operating below thermoelectrical cooling. AlAsSb with Sb composition, xSb = 0.97; barrier doping, ND < 2×1016 cm?3 leading to valence band offset below 100 meV in relation to the active layer doping, ND = 5×1015 cm?3 was proved to be proper material not introducing extra barrier in valence band in the analyzed temperature range in XBn architectures. The detectivity of the simulated structure was assessed at the level of ~ 1011 Jones at T ~ 100 K assuming absorber thickness, d = 3 μm. The detector’s architecture for high frequency response operation, τs = 420 ps (T ~ 77 K) was presented with a reduced active layer of d = 1 μm.  相似文献   

13.
研究了GaSb/GaAs复合应力缓冲层上自组装生长的InAs量子点.在2ML GaSb/1ML GaAs复合应力缓冲层上获得了高密度的、沿[100]方向择优分布量子点.随着复合应力缓冲层中GaAs层厚度的不同,量子点的密度可以在1.2×1010cm-2和8×1010cm-2进行调控.适当增加GaAs层的厚度至5ML,量子点的发光波长红移了约25nm,室温下PL光谱波长接近1300nm. 关键词: 自组装量子点 分子束外延 Ⅲ-Ⅴ族化合物半导体  相似文献   

14.
GaAs lattice “superdilation” caused by an introduced tellurium impurity, which is well known in publications, is experimentally studied. This phenomenon consists in the fact that the GaAs-lattice dilation can be more than 10 times greater than expansion that would appear upon the replacement of arsenic atoms with tellurium atoms if calculations are performed using the current-carrier concentration and Vegard’s law. The given phenomenon has already been observed at n Te > 3 × 1018 cm–3. A series of GaAs epitaxial layers heavily doped with tellurium and grown via metal-organic chemical vapor deposition are investigated using high-resolution X-ray diffractometry (HRXRD), secondary-ion mass spectrometry (SIMS), and the Hall effect. It is demonstrated that, despite a high Te concentration (1020?1021 cm–3) in the layer and variations in the growth conditions, the concentration estimates based on HRXRD data depend linearly on the results of elemental analysis performed by means of SIMS. The GaAs lattice expands even somewhat slighter as compared to the case where arsenic atoms are replaced with all Te atoms injected into the layer. At the same time, the Hall carrier concentration decreases sharply beginning at 2 × 1020 cm–3. In accordance with the obtained results, the examined phenomenon can be interpreted as the strong compensation of donor and acceptor carriers rather than as superdilation.  相似文献   

15.
The effect of interface anisotropy on the electronic structure of InAs/GaSb type-II superlattices is exploited in the design of thin-layer superlattices for mid-IR detection threshold. The design is based on a theoretical envelope function model that incorporates the change of anion and cation species across InAs/GaSb interfaces, in particular, across the preferred InSb interface. The model predicts that a given threshold can be reached for a range of superlattice periods with InAs and GaSb layers as thin as a few monolayers. Although the oscillator strengths are predicted to be larger for thinner period superlattices, the absorption coefficients are comparable because of the compensating effect of larger band widths. However, larger intervalence band separations for thinner-period samples should lead to longer minority electron Auger lifetimes and higher operating temperatures in p-type SLs. In addition, the hole masses for thinner-period samples are on the order the free-electron mass rather than being effectively infinite for the wider period samples. Therefore, holes should also contribute to photoresponse. A number of superlattices with periods ranging from 50.6 to 21.2 Å for the 4 μm detection threshold were grown by molecular beam epitaxy based on the model design. Low temperature photoluminescence and photoresponse spectra confirmed that the superlattice band gaps remained constant at 330 meV although the period changed by the factor of 2.5. Overall, the present study points to the importance of interfaces as a tool in the design and growth of thin superlattices for mid-IR detectors for room temperature operation.  相似文献   

16.
Doping superlattices show tunable optical and electrical properties due to the space charge induced separation of photoexcited or electrically injected carriers. We have investigated the tunable luminescence in GaAs doping superlattices of doping levels n=1×1018cm−3 and n=4×10 18cm−3 as function of excitation density and sample temperature. The temperature dependence of the tunability was investigated in the range between 4 and 700K, and we found the critical transition temperatures T0 at 90 and 460K for the low and high doped samples, respectively. The results verify the theoretical prediction concerning the transition temperature at which the luminescence changes from full to zero tunability.  相似文献   

17.
Abstract

Optical absorption bands and epr spectra of NaCl: Mn++ X-irradiated at liquid nitrogen and room temperature are studied. Manganese epr spectra are divided into three classes, based on the value of hyperfme splitting constants. It is shown that the epr spectra with the hyperhe splitting constants of around 250 × 10-4, 80 × 10?4 and 20 × 10?4 cm?1 are caused by Mn+, Mn++ and Mn9, respectively. Formation of several manganese centers by X-irradiation is discussed. It is suggested that optical absorption bands at 410 and 440 nm are caused by MnO at the lattice site and that the MnO center which gives an epr spectrum with A = 15. 5 × 10?4 cm?1 is associated with a Mn0 center which is not at a substitutional site.  相似文献   

18.
Single crystal 400 nm thick Laves phase [20 Å?DyFe2/80 Å?YFe2]40 superlattice have been grown by MBE with a (110) growth direction. VSM measurements performed at room temperature with an applied field range of ±1.2×105 Oe, directed along the [001] direction, reveal a unique single-phase-liked ferrimagnetic behavior. A dominant exchange spring behavior is revealed by MOKE measurement along the [–110] direction. Furthermore, for striped arrays patterned along the [001] direction with height-to-width ratio of 0.05, a shape anisotropy of the order of 104 erg/cm3 is induced, resulting into a pronounced change of coercivity due to the comparable magnitude with intrinsic anisotropies. The results demonstrate the feasibility of engineering both single-phase-liked and exchange-spring magnet behavior in Laves phase epitaxial hard/soft superlattices by patterning.  相似文献   

19.
X-band electron paramagnetic resonance (EPR) study of Cr3+-doped dipotassium tetrachloropalladate single crystal is done at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters have been evaluated by employing hyperfine resonance lines observed in EPR spectra for different orientations of crystal in externally applied magnetic field. The values of spin-Hamiltonian and zero-field splitting (ZFS) parameters of Cr3+ ion-doped DTP for site I are: g x  = 2.096 ± 0.002, g y  = 2.167 ± 0.002, g z  = 2.220 ± 0.002, D = (89 ± 2) × 10?4 cm?1, E = (16 ± 2) × 10?4 cm?1. EPR study indicates that Cr3+ ion enters the host lattice substitutionally replacing K+ ion and local site symmetry reduces to orthorhombic. Optical absorption spectra are recorded at room temperature. From the optical absorption study, the Racah parameters (B = 521 cm?1, C = 2,861 cm?1), cubic crystal field splitting parameter (Dq = 1,851 cm?1) and nephelauxetic parameters (h = 2.06, k = 0.21) are determined. These parameters together with EPR data are used to discuss the nature of bonding in the crystal.  相似文献   

20.
We report calculated electron impact ionization cross sections (EICSs) for beryllium (Be) and some of its hydrides from the ionization threshold to 1 keV using the Deutsch-Märk (DM) and the Binary-Encounter-Bethe (BEB) formalisms. The positions of the maxima of the DM and BEB cross sections are very close in each case while the DM cross section values at the maxima are consistently higher. Our calculations for Be are in qualitative agreement with results from earlier calculations (convergent close-coupling, R matrix, distorted-wave and plane-wave Born approximation) in the low energy region. For the various beryllium hydrides, we know of no other available data. The maximum cross section values for the various compounds range from 4.0 × 10?16 to 9.4 × 10?16 cm2 at energies of 44 to 56 eV for the DM cross sections and 3.0 × 10?16 to 5.4 × 10?16 cm2 at energies of 40.5 to 60 eV for the BEB cross sections.  相似文献   

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