IntegratedIn Situ wafer and system monitoring for the growth of CdTe/ZnTe/GaAs/Si for mercury cadmium telluride epitaxy

Reproducible improvements in the metalorganic vapor phase epitaxy (MOVPE) grown CdTe buffer quality have been demonstrated in a horizontal rectangular duct silica reactor by the use of integratedin situ monitoring that includes laser reflectometry, pyrometry, and Epison concentration monitoring. Specular He-Ne laser reflectance was used toin situ monitor the growth rates, layer thickness, and morphology for both ZnTe and CdTe. The substrate surface temperature was monitored using a pyrometer which was sensitive to the 2–2.6 μm waveband and accurate to ±1°C. The group II and group VI precursor concentrations entering the reactor cell were measured simultaneously using two Epison ultrasonic monitors and significant variations were observed with time, in particular for DIPTe. The surface morphology and growth rates were studied as a function of VI/II ratio for temperatures between 380 and 460°C. The background morphology was the smoothest for VI/IIratio in the vicinity of 1.5–1.75 and could be maintained using Epison monitors. Regularly shaped morphological defects were found to be associated with morphological defects in the GaAs/Si substrate. The x-ray rocking curve widths for CuK_α (531) reflections were in the range of 2.3–3.6 arc-min, with no clear trend with changing VI/II ratio. X-ray topography images of CdTe buffer layers on GaAs/Si showed a mosaic structure that is similar to CdTe/sapphire substrates. The etch pit density in Hg_1-xCd_xTe layers grown onto improved buffer layers was as low as 6 x 10⁶ cm^-2 for low temperature MOVPE growth using the interdiffused multilayer process.     

Effect of annealing in N2 atmosphere on net acceptor concentration in ZnSe:N grown by MOCVD

Annealing effect on net acceptor concentration in ZnSe:N is investigated. ZnSe:N homo-epitaxial layer was grown at 823 K by MOCVD using ammonia (NH₃) as a dopant source. Photoluminescence (PL) spectra measured on as-grown layer exhibited the strong deep donor–acceptor pair (D^dAP) emission and the weak I₁^N emission line. In order to enhance the activation of nitrogen in ZnSe epitaxial layer, sample was annealed at the 823 K in nitrogen (N₂) and hydrogen (H₂) atmosphere. Only the annealing in nitrogen atmosphere increased I₁^N emission intensity indicate the activation of nitrogen acceptor. And net acceptor concentration was estimated to be 3 × 10¹⁷cm⁻³ by C–V measurements. This activation mechanism is interpreted as hydrogen is released from N–H bonds during annealing in nitrogen atmosphere.     

Electrical and photo-luminescence properties of ZnSe epitaxial layers grown on GaAs (100) by atmospheric pressure MOVPE: The role of substrate temperature

Epitaxial layers of ZnSe ranging in thickness from 5μm to 30 μm have been grown on GaAs (100) substrates over the temperature range 240° C to 340° C by atmospheric pressure MOVPE employing dimethylzinc and hydrogen selenide. An optimum growth temperature of 280 ± 5° C has been identified and when grown at this temperature the ZnSe epitaxial layers exhibit low resistivity (ρ_{298 K} ≤ 10 ohm · cm), a low compensation ratio (θ_{298 K} = 0.27), a carrier mobility (μ_{298 K}) of 250 ±10 cm²V^-1s^-1) and aren-type (n _{298 K} = 8.0 × 10¹⁴ cm^-3). The ratio of photoluminescence intensity measured at 298K and at 12 K is high (10⁴) and is dominated by a sharp emission due to excitons bound to neutral donors at 2.7956 eV. Mass spectrometric investigations of the chemical reactions occurring inside the reactor in the presence of the GaAs substrate indicate significant surface-controlled reactivity in the region of 280° C.     

浅ZnCdSe/ZnSe量子阱的光泵受激发射

本文主要研究浅ZnCdSe/ZnSe单量子阱在77K温度下的光致发光。在不同激发密度下,讨论了该结构的发光机制,把77K温度下的受激发射归结为是激子-激子散射所引起的。文中还分析了在浅ZnCdSe/ZnSe量子阱中能够实现与激子相关的受激发射的原因。     

Irregular shifts of excitonic states in reflectivity and PL spectra of ZnSe crystals under uniaxial stress

Splittings and shifts of excitonic states in ZnSe crystals under uniaxial stress along [100], [111] and [110] directions were studied by spatially resolved spectroscopy of both the reflectivity and the photoluminescence (PL) at 5 K. These methods enabled us to check the local strains in different surface microareas of deformed crystals and as a result to reveal the irregular free and bound exciton state shifts related to the influence of the strain nonuniformity and to the presence of structural imperfections (twins) in the crystals. It is shown that elastic deformation of twinned crystals along directions not exactly [111] gives rise to a doublet structure for all the bound exciton lines in the PL spectra. New values of deformation potentials for ZnSe crystals were deduced. The anisotropic influence of the uniaxial stress on the free and bound exciton state splittings was determined.     

ZnMgSSe/ZnSSe/ZnSe-heterostructures grown by metalorganic vapor phase epitaxy

ZnMgSSe heterostructures have been grown in a low-pressure metalorganic vapor phase epitaxy system with the precursors dimethylzinc triethylamine, ditertiarybutylselenide, tertiarybutylthiol, and biscyclopentadienylmagnesium at 330°C and a total pressure of 400 hPa. The optimization of the single layers was carried out by means of low temperature photoluminescence. Only the near band edge emission was observable with negligible deep levels. The heterostructures consisting of a triple ZnSe quantum well showed intense luminescence which hints at an effective carrier confinement. Scanning transmission electron microscopy investigations of the heterostructures still showed structural detects since the layers were not lattice matched to the GaAs substrate yet.     

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.     

Surface treatment of znse substrate and homoepitaxy of znse

High quality ZnSe(100) substrates have been used for homoepitaxial growth by molecular beam epitaxy. A chemical pretreatment suitable for ZnSe substrate preparation is determined from x-ray photoemission spectroscopy studies. Thermal cleaning processes for the ZnSe(100) surface were investigated by insitu reflection high energy electron diffraction and the surface phase diagram for ZnSe(100) was obtained for the first time. The low temperature photoluminescence spectra recorded from homoepitaxial layers exhibit unsplit free and bound exciton transitions with strong intensities. The full widths at half maximum of the (400) x-ray diffraction spectra for ZnSe homoepitaxial layer were 17≈31 arcsec.     

Zn0.8Cd0.2Se-ZnSe应变层超晶格的激子发光和受激发射

本文用MOCVD技术在GaAs衬底上成功地制备了具有波导结构的Zn0.8Cd0.2Se-ZnSe应变层超晶格样品,在77K温度的光致发光光谱中观测到n=1的重空穴和轻空穴激子的辐射复合。在光泵浦下,在波导结构的F-P腔中观测到具有多模结构的受激发射,受激发射谱中的不同模具有不同的阈值功率密度;时间延迟衰减曲线的半宽度越窄,阈值光强越大.     

Carbon and hydrogen incorporation in ZnTe layers grown by metalorganic chemical vapor deposition

The metalorganic chemical vapor deposition growth of ZnTe has been performed at atmospheric pressure under helium and hydrogen carrier gases. Epitaxial growth was achieved on GaAs (100) substrates with the combination of diethylzinc and diethyltellurium as precursors. We have studied the incorporation of carbon and hydrogen in as-grown layers of ZnTe by secondary ion mass spectroscopy analysis and out-diffusion experiments with different carrier gases and growth temperatures. The amount of carbon and hydrogen incorporated in the ZnTe layers greatly depends on the nature of the gas considered. Under helium atmosphere, the amount of carbon and hydrogen incorporated are greater than under H₂ with an origin from organometallic precursors.