Solid source MBE growth of InAsP/InP quantum wells

Strained InAsP multiquantum wells (MWQs) were grown on InP(100) substrates by solid source molecular beam epitaxy and were characterized to relate structural and optical quality to growth conditions. The multiquantum wells were grown using either dimer or tetramer arsenic (As₂ or As₄) over the substrate temperature range of 420–535°C. θ-2θ x-ray diffraction measurements showed only slight differences between arsenic compositions in the quantum wells grown with As₂ or As₄. 300K and 8K photoluminescence full width at half max (FWHM) decreased at higher growth temperatures regardless of the arsenic species used. The 8K photoluminescence FWHM and the surface roughness measured by atomic force microscopy are found to be less sensitive to substrate growth temperature for the multiquantum wells growth with As₂ as opposed to As₄.     

Antisite arsenic incorporation in the low temperature MBE of gallium arsenide: Physics and modeling

A stochastic model for simulating the surface growth processes in the low temperature molecular beam epitaxy of gallium arsenide is developed to investigate the incorporation of antisite As and its dependence on the growth conditions including the dynamics of the physisorbed As on the surface. Three different kinetic models with a combination of surface kinetic processes such as incorporation of antisite As, evaporation of antisite As and incorporation of regular As. The kinetic model with all three surface processes was accepted as the best model due to its physical soundness and reasonableness of its model parameters. The arsenic flux, temperature, and growth rate dependences of antisite arsenic (As_Ga) obtained from our simulation are in excellent agreement with the experimental results. The activation energy of 1.16 eV and a frequency factor of 4×10¹²/s for the evaporation of antisite arsenic obtained from our model are in good agreement with experimental and theoretical estimates. At a constant substrate temperature and growth rate, the antisite arsenic concentration increases with arsenic flux for low fluxes and saturates beyond a critical flux. The critical arsenic flux increases with temperature and the saturation value of the As_Ga concentration decreases with temperature. As the arsenic flux increases, the coverage of the physisorbed layer increases and at a critical flux dictated by the fixed temperature and growth rate, the coverage saturates at its maximum value of unity (a complete monolayer) and hence the concentration of As_Ga saturates. Lower As_Ga concentration results at higher temperature due to more evaporation of As_Ga. Additionally, an analytical model is developed to predict the As_Ga concentration for various growth conditions.     

Arsenic incorporation in MBE grown Hg1−xCdxTe

The p-type doping of Hg_1−xCd_xTe (MCT) has proven to be a significant challenge in present day MCT-based detector technology. One of the most promising acceptor candidates, arsenic, behaves as an amphoteric dopant which can be activated as an acceptor during Hg-rich, low temperature annealing of as-grown molecular beam epitaxy (MBE) samples. This study focuses on developing an understanding of the microscopic behavior of arsenic incorporation during MBE growth. In particular, the question of whether arsenic incorporates as individual As atoms, as As₂ dimers, or as As₄ tetramers is addressed for MBE growth with an As₄ source. A quasithermodynamical model is employed to describe the MCT growth and As incorporation, with parameters fitted to an extensive database of samples grown at the Microphysics Laboratory. The best fits for growth temperatures between 175 and 185°C are obtained for arsenic incorporation as As₄ or possibly as As₄ clusters, with lower probabilities for As₂ and individual As atoms. Based on these results, we investigate the relaxed atomic configurations of As₄ and As₂ in bulk HgTe by ab initio total energy calculations. The calculations are performed in the pseudopotential density-functional framework within the local density approximation, employing supercells with periodic boundary conditions. The lattice distortions due to As₄ and As₂ in bulk HgTe are predicted to be modest due to the small size of these arsenic clusters.     

Doping of molecular beam epitaxy HgCdTe using an arsenic cracker source (As2)

This study investigated the incorporation of arsenic dimers (As₂), delivered from a “cracker” effusion cell. The HgCdTe epilayers were deposited under standard growth conditions. During deposition, arsenic was incorporated using both a standard arsenic effusion cell and a cracker cell. It was found that arsenic concentration rose dramatically as a function of cracker-zone temperature, particularly at temperatures above 600°C. This behavior was consistent with the temperature dependence of the effusion cell’s cracking efficiency, as determined by residual gas analysis. The temporal stability of the arsenic source was excellent. Arsenic concentrations of 2.8×10²⁰ cm⁻³ were achieved at a cracker temperature of 800°C. The arsenic beam-equivalent pressure, estimated from an uncorrected, nude ion-gauge reading, was ∼8×10⁻⁷ mbar.     

Interfaces of InAsP/InP multiple quantum wells grown by metalorganic vapor phase epitaxy

We present results of the growth of InAs_xP_1−x/InP strained heterostructures by low pressure metalorganic vapor phase epitaxy. A large incorporation of arsenic into the InAsP ternary was observed using tertiarylbutylarsine as precursor. High resolution x-ray diffraction, photoluminescence, and optical absorption measurements for InAsP/InP strained multiple quantum wells reveal that the InAsP/InP interface is very sensitive to growth interruption. A systematic study of a growth in terruption sequence designed to improve the InAs/InP interface was carried out. For nonoptimal growth interruption procedures a large density of interface states is created, probably as a consequence of compositional modifications within the interface region. We find that the absorption spectrum may reveal a significant density of interface states. Thus, photoluminescence on its own is insufficient to characterize the interface roughness even for structures showing narrow low-temperature photoluminescence peaks. We also observe an enhancement of the As content for structures grown on InP (001) relative to those simultaneously grown on InP(001) two degrees off toward [100], which suggests that the composition of As in the ternary is limited by its surface diffusion.     

Chemical vapor deposition of B12As2 thin films on 6H-SiC

Icosahedral boron arsenide (B₁₂As₂) thin films were deposited on 6H-SiC substrates by chemical vapor deposition using B₂H₆ and AsH₃ sources. X-ray diffraction analysis of the thin films showed them to have the rhombohedral crystal structure and lattice parameters of B₁₂As₂. Transmission electron microscopy showed that the films were polycrystalline with oriented crystal grains. The preferential orientation of the film with respect to the SiC substrate was determined to be: [0001]_B12_{As 2}//[0001]_6H-SiC and [ ]_B12_{As 2}//[ ]_6H-SiC to within 3°. Electron diffraction also revealed the extremely small lattice mismatch (<0.5%) between the B₁₂As₂ basal-plane lattice parameter and twice the SiC basal-plane lattice parameter.     

Microscopic Origin of Electrical Compensation in Arsenic-Doped HgCdTe by Molecular Beam Epitaxy: Density Functional Study

The understanding of the configurations of the arsenic tetramer (As _t ), dimer (As _d ), and singlet (As _s ) is important to explain the high electrical compensation of molecular beam epitaxy (MBE) samples and the conversion to p-type behavior. In this work, the possible configurations were optimized from density functional calculations for arsenic defects As _n (n = 1, 2, and 4) in as-grown HgTe. According to the dominant electronic contribution to the defect formation energies, which was calculated under Te-rich conditions, the most probable configurations for As _t , As _d , and As _s have been established. The above discussion applies to the neutral arsenic defects. A further study is necessary to consider the entropy contribution to the defect formation energy.     

The effect of trimethylaluminum concentration on the incorporation of P In AlxGa1−xPyAs1−y grown by organometallic vapor phase epitaxy

The organometallic vapor phase epitaxial (OM-VPE) growth of Al_xGa_1-xP_yAs_1-y on graded GaP_yAs_1-yGaAs in the compositional range 0 < x < 0.9 and 0 < y < 0.6 is reported. It is found that composition control can be easily achieved, and that the vapor phase ratio of trimethylaluminum to trimethylgallium strongly influences the incorporation of P in the solid. A model is developed which explains this in terms of competing reaction rates. The model gives a good fit to the experimental data.     

Unintentional As incorporation in molecular beam epitaxially grown InAs/AlSb/GaSb heterostructures

We investigate unintentional arsenic incorporation during the molecular-beam epitaxial growth of AlSb/InAs/GaSb heterostructures, using both a standard As₄ evaporation cell and a valved arsenic cracker. When a standard As₄ cell is used, unintentional arsenic concentrations as large as 10–20% can be incorporated into the AlSb and GaSb layers from the background As ambient in the growth chamber, both during growth and on stationary surfaces. This incorporation can be controlled and suppressed with the use of a valved As cracker. Suppression of the As background substantially improves the electrical transport properties of AlSb/InAs/AlSb quantum well structures.     

Group-V composition control for InGaAsP grown by gas source molecular beam epitaxy

Based on our kinetics models for gas source molecular beam epitaxy of mixed group-V ternary materials, the group-V composition control in In_yGa_1−yAs_1−xP_x epilayers has been studied. The P or As composition in In_yGa_1−yAs_1−xP_x (lattice matched to InP or GaAs) can be obtained from a simple equation for substrate temperatures below 500°C. This has been verified by a series of experimental results.     

Carbon doping and etching in GaxIn1−xAsyP1−y on GaAs substrates using CBr4 by metalorganic chemical vapor deposition

Carbon doping and etching by CBr₄ were studied for Ga_xIn_1−xAs_yP_1−y (0≤y≤1) on GaAs grown by metalorganic chemical vapor deposition. It was found that the hole concentration drastically decreases with decreasing y when the flow rate of CBr₄ is constant. When y is under 0.5, the conduction type of GaInAsP changes ton-type. In the region of 0<y<0.6, the surface morphology was degraded and the carrier compensation became higher than could be estimated from the C concentration. This seems to be due to the micro defects because this range of composition is within the unstable region which is theoretically predicted. The etching effect by CBr₄ was observed during the growth. The rate of etching for InAsP component is about three times larger than that for the GaAsP component. The thermodynamic analysis suggests that the etching is due to the increase of the partial pressure of GaBr and InBr.     

掺砷碲镉汞的研究进展

掺砷碲镉汞是一科用于制作p-on-n器件和实现高性能碲镉汞探测器及多色红外焦平面阵列的关键材料。对掺砷碲镉汞的相关文献进行了归纳分析。砷渺活效率与退火条件及砷的浓度直接相关。对于掺砷浓度在10^16-10^18cm-3范围内的碲镉汞,通过300℃／16h和240℃／4sh两步退火可将样品前表面激活为P型材料,但汞空位的浓度相对于背面较高。样品背面靠近衬底处可能存在AsT和AsHg缺陷。     

Electrical properties of InAlAs/InAsxP1-x/InP composite-channel modulation-doped structures grown by solid source molecular beam epitaxy

We report on the electrical characteristics of the two-dimensional electron gas (2DEG) formed in an InAlAs/InAs_xP_1-x/InP pseudomorphic composite-channel modulation-doped (MD) structure grown by solid source (arsenic and phosphorus) molecular beam epitaxy (SSMBE). The As composition, x, of strained InAs_xP_1-x was determined by x-ray diffraction analysis of InP/InAs_xP_1-x/InP multi-quantum wells (MQWs) with compositions of x=0.14 to x=0.72. As the As composition increases, the room temperature sheet resistance of InAlAs/InAs_xP_1-x/InP composite-channel MD structures grown over a range of As compositions decreased from 510 to 250 Ω/cm², resulting from the greater 2DEG confinement and lower electron effective mass in the InAs_xP_1-x channel as x increases. The influence of growth conditions and epitaxial layer designs on the 2DEG mobility and concentration were investigated using 300 K and 77 K Hall measurements. As the exposure time of the As₄ flux on the growth front of InAs_xP_1-x increased during growth interruptions, the 2DEG mobility, in particular the 77K mobility, was considerably degraded due to increased roughness at the InAlAs/InAs_xP_1-x interface. For the InAlAs/InAs_0.6P_0.4/InP composite-channel MD structure with a spacer thickness of 8 nm, the room temperature 2DEG mobility and density were 7200 cm²/Vs and 2.5 × 10¹² cm⁻², respectively. These results show the great potential of the InAlAs/InAs_xP_1-x/InP pseudomorphic composite-channel MD heterostructure for high frequency, power device applications.     

Low pressure metalorganic chemical vapor deposition of InP and related compounds

The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga_0.47In_0.53 As and Ga_xIn_1-xAs_yP_1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm² V⁻¹S⁻¹ at 300 K and 58 900 cm² V⁻¹ S⁻¹ at 77₂K, and for GaInAs was 11900 cm² V⁻¹ S⁻¹ at 300 K, 54 600 cm² V⁻¹ S⁻¹ at 77 K and 90 000 cm V⁻¹S⁻¹ at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current.     

Diffusion of zinc into gaas layers grown by molecular beam epitaxy at low substrate temperatures

We report the diffusion of zinc into low temperature (LT) GaAs grown by MBE at 200° C, the problems associated with using a silicon nitride film directly deposited on the LT GaAs as a Zn diffusion mask, and several schemes to avoid the problems. The Zn diffusion coefficient is measured (sealed-ampoule technique) to be about one order of magnitude higher in the LT GaAs than in normal GaAs, attributed to a large quantity of defects including arsenic antisites (As_Ga) in the LT GaAs. The effectiveness of silicon nitride as a Zn diffusion mask depends if the mask is deposited directly on the LT GaAs. The failure of the nitride directly deposited on the LT GaAs to stop the Zn is attributed to arsenic atoms outdiffusing from the As-rich LT GaAs (about 1 at. % excess As) into the nitride. Several structures are introduced including a 100-Å thick GaAs layer on the LT GaAs that are effective in preserving the diffusion mask properties of the silicon nitride.     

Growth and characterization of heavily carbon doped InGaAs lattice matched to InP by LP-MOCVD using liquid CCI4

The growth of heavily carbon dopedp-InGaAs (~6.5xl0¹⁹cm^-3) lattice-matched to InP is reported. Growth is achieved by low pressure metalorganic chemical vapor deposition (LP-MOCVD) using all methyl metalorganic sources and liquid CC1₄. The impact of growth temperature and CC1₄ flow rates on growth rate reduction and alloy compositional change was investigated. Post-growth isothermal and isochronal annealing experiments were performed on the carbon doped InGaAs layers and a quantitative analysis of carrier activation is presented using Hall and secondary ion mass spectroscopy measurements. Reduced self-compensation by carbon displacement from indium to arsenic site, as well as, reduced hydrogen passivation are suggested as possible mechanisms responsible for carrier activation upon thermal annealing.     

Calculation of energy band gaps in quaternary iii/v alloys

The dielectric theory of electronegativity is applied to the calculation of the compositional dependence of the energy band gap for quaternary III/V alloys of type A_l-xB_xC_1-yD_y and A_1-x-yB_xC_yD. The departure from linearity of E_G versus x and y is taken to be the sum of two terms, the intrinsic or virtual crystal term and the extrinsic term due to effects of aperiodicity which for one type of alloy may occur on both sublattices. Rather than simply treating the quaternary as an average of the bounding ternary systems, as has been common in the past, the intrinsic departure from linearity is calculated by assuming E_h,i,C, and D_av to vary linearly with x and y. The result is a smaller intrinsic deviation from linearity and a much better fit to existing data in the system Ga_1-xIn_xAs_1-y P_y. The calculation is also applied to three systems where no data exist but which are of great interest because of their potential application for the fabrication of lattice matched tandem solar cells: Ga_l-xA1_xAs_l-ySb_y. Ga_1-x-yA1_xIn_yAs, and GaAs_1-x-yP_xSb_y.     

MBE growth and characterization of in situ arsenic doped HgCdTe

We report the results of in situ arsenic doping by molecular beam epitaxy using an elemental arsenic source. Single Hg_1−xCd_xTe layers of x ∼0.3 were grown at a lower growth temperature of 175°C to increase the arsenic incorporation into the layers. Layers grown at 175°C have shown typical etch pit densities of 2E6 with achievable densities as low as 7E4cm⁻². Void defect densities can routinely be achieved at levels below 1000 cm⁻². Double crystal x-ray diffraction rocking curves exhibit typical full width at half-maximum values of 23 arcsec indicating high structural quality. Arsenic incorporation into the HgCdTe layers was confirmed using secondary ion mass spectrometry. Isothermal annealing of HgCdTe:As layers at temperatures of either 436 or 300°C results in activation of the arsenic at concentrations ranging from 2E16 to 2E18 cm⁻³. Theoretical fits to variable temperature Hall measurements indicate that layers are not compensated, with near 100% activation after isothermal anneals at 436 or 300°C. Arsenic activation energies and 77K minority carrier lifetime measurements are consistent with published literature values. SIMS analyses of annealed arsenic doping profiles confirm a low arsenic diffusion coefficient.     

In situ P-doped Si and Si1−xGex epitaxial films grown by remote plasma enhanced chemical vapor deposition

Remote plasma-enhanced chemical vapor deposition has been applied to growin- situ doped n-type epitaxial Si and Si_1−xGe_x with the introduction of phosphine. Growth rates and dopant incorporation have been studied as a function of process parameters (temperature, rf power, and dopant gas flow). Growth rates remain unaltered with the introduction of PH₃ during deposition, unlike in many other low temperature growth techniques. Phosphorus incorporation shows a linear dependence on PH₃ flow rate, but has little if any dependence on the other growth parameters, such as radio frequency power and substrate temperature, for the ranges of parameters that were examined. Phosphorus concentrations as high as 4 × 10¹⁹ cm⁻³ at 14 W have been obtained.