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.     

MBE growth and characterization of high purity GaAs/AIGaAs on the (110) surface of GaAs

An improved quality of (110) GaAs has been grown by molecular beam epitaxy using As₂ in lieu of As₄. The most pronounced effect of using As₂ is a higher doping efficiency of Si δ-doped GaAs layers, resulting in a mobility of the (110) layers, comparable to the reference (100) samples.

The high quality of the (110) GaAs was confirmed by low temperature photoluminescence. The spectrum of the GaAs layer shows a single dominant free exciton line with a linewidth of 1.0 meV.     

Excitons in single and double GaAs/AlGaAs/ZnSe/Zn(Cd)MnSe heterovalent quantum wells

Exciton photoluminescence spectra, photoluminescence excitation spectra, and magnetophotoluminescence spectra of single (GaAs/AlGaAs/ZnMnSe) and double (GaAs/AlGaAs/ZnSe/ZnCdMnSe) heterovalent quantum wells formed by molecular beam epitaxy are studied. It is shown that the exciton absorption spectrum of such quantum wells mainly reproduces the resonant exciton spectrum expected for usual quantum wells with similar parameters, while the radiative exciton recombination have substantial distinctions, in particular the additional localization mechanism determined by defects generated by heterovalent interface exists. The nature of these localization centers is not currently clarified; their presence leads to broadening of photoluminescence lines and to an increase in the Stokes shift between the peaks of luminescence and absorption, as well as determining the variation in the magnetic g factor of bound exciton complexes.     

Electrical and optical properties of lodine doped CdZnTe layers grown by metalorganic vapor phase epitaxy

Electrical and photoluminescence properties of iodine doped CdZnTe (CZT) layers grown by metalorganic vapor phase epitaxy have been studied. Doped layers showed an n-type conductivity from the Zn composition x=0 (CdTe) to 0.07. Above x=0.07, resistivities of doped layers increased steeply up to 10⁶ Ω-cm. Resistivities of doped CZT layers were higher than those of undoped layers above x=0.6. Photoluminescence intensity of doped layers increased compared to undoped layers. Doped CdTe and ZnTe layers showed neutral donor bound exciton emission lines at the exciton related region. Also, these layers showed an increase in emission intensity at the donor acceptor pair recombination bands. Sharp emission lines were observed in doped CZT layers at around 1.49 eV. These emission lines were considered to be originated from GaAs substrates which were optically excited by the intense emission from doped CZT layers.     

Optical properties of undoped and iodine-doped CdTe

A comprehensive study of the properties of undoped and iodine-doped CdTe structures by photoluminescence (PL) and photoreflectance (PR) is reported. Undoped bulk CdTe and iodine-doped CdTe layers grown by metalorganic molecular beam epitaxy on (lOO)-oriented CdTe and (211)B-oriented GaAs substrates with electron concentrations ranging from 10¹⁴ to mid-10¹⁸ cm^-3 were included in this study. Lineshape modeling of 80KPL and PR spectra indicated the presence of both free exciton and donor-hole transitions at the higher doping levels. Strong PL and PR signals were also observed at room temperature. If only a single transition is considered for the analysis of the 300K spectra, the PL emission peak and the PR transition energy both exhibit a strong dependence on electron concentration for doped layers. However, lineshape modeling of the room-temperature spectra indicated the presence of multiple transitions consisting of free exciton and direct band-to-band transitions. The use of two transitions resulted in a constant value of bandgap over the entire range of conductivities studied. A strong correlation remained between the broadening of the PR and PL spectra and excess carrier concentration N_D-N_A. In addition, the E₁ transition energy measured by PR was found to vary dramatically with growth conditions.     

Photoluminescence of Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te based heterostructures grown by molecular-beam epitaxy

Photoluminescence (PL) of Hg_{1 − x} Cd _x Te-based heterostructures grown by molecular-beam epitaxy (MBE) on GaAs and Si substrates has been studied. It is shown that a pronounced disruption of the long-range order in the crystal lattice is characteristic of structures of this kind. It is demonstrated that the observed disordering is mostly due to the nonequilibrium nature of MBE and can be partly eliminated by postgrowth thermal annealing. Low-temperature spectra of epitaxial layers and structures with wide potential wells are dominated by the recombination peak of an exciton localized in density-of-states tails; the energy of this peak is substantially lower than the energy gap. In quantum-well (QW) structures at low temperatures, the main PL peak is due to carrier recombination between QW levels and the energy of the emitted photon is strictly determined by the effective (with the QW levels taken into account) energy gap.     

Optical transmittance of thin GaAs wafers upon laser pumping in the region of exciton resonances and the continuum of states: Exciton-exciton interaction

The transmittance spectra of thin “pure” GaAs bulk wafers upon optical pumping corresponding to the band of the ground state of the exciton series are recorded at a temperature of T = 1.7 K. The wafers were grown by molecular-beam epitaxy and vapor-phase epitaxy. An increase in the line amplitude and width upon pumping is observed, with no noticeable changes in the spectral position of the line peak. The increase is similar to that observed upon pumping in the continuum of states, but occurs at a somewhat lower rate. Estimation of the concentration of excitons created by pumping provides a means for determining the exciton-exciton interaction constant and comparing the result with known data. The integrated absorption method makes it possible to refine the exciton polariton-free charge carrier and exciton polariton-impurity interaction constants. The differential photoabsorption of the samples at the pumping modulation frequency is measured. The resultant modulated absorption spectra demonstrate the connection between induced absorption and the formation of differential spectra.     

Dependence of the concentration of ionized donors on epitaxy temperature for Si:Er/Si layers grown by sublimation molecular-beam epitaxy

The dependence of the concentrations of the Er impurity and ionized donors on the epitaxy temperature has been studied before and after annealing of Si:Er/Si layers grown by sublimation molecular-beam epitaxy. n-Si:Er layers have been grown in the temperature range 400–800°C and annealed in hydrogen atmosphere at a temperature of 800°C for 30 min. The possible nature of the donor centers is discussed.     

Doping of gallium nitride using disilane

The silicon doping of n-type GaN using disilane has been demonstrated for films grown on sapphire substrates by low pressure organometallic vapor phase epitaxy. The binding energy of an exciton bound to a neutral Si donor has been determined from low temperature (6K) photoluminescence spectra to be 8.6 meV. Nearly complete activation of the Si impurity atom in the GaN lattice has been observed.     

量子限制效应对受主跃迁的影响

通过光致发光光谱,研究了量子限制效应对GaAs体材料中均匀掺杂和一系列GaAs/AlAs多量子阱(阱宽范围从30A到200A)中δ-掺杂浅受主杂质铍(Be)原子带间跃迁的影响.实验中所用的样品是利用分子束外延技术生长的均匀掺Be受主的GaAs外延层和一系列在量子阱的中央进行了浅受主Be原子δ-掺杂的GaAs/AlAs多量子阱.在4.2K的低温下,测量了上述样品的光致发光谱,很清楚地观察到了受主束缚激子从基态1S3/2(Γ6)到两个激发态2S3/2(Γ6)和3S3/2(Γ6)的双空穴跃迁.研究发现,随着量子限制效应的增强,受主跃迁能量会增加.对量子限制效应调节受主杂质问跃迁能量的研究,进一步增强了对受主能态可调性的认识,为太赫兹远红外发光器或激光器的研发提供了一种新的途径.     

Investigations on indium phosphide grown by chemical beam epitaxy

In this paper, we present a systematic study of the properties of indium phosphide (InP) layers grown by chemical beam epitaxy (CBE). Trimethylindium (TMIn) and phosphine (PH₃) are used as source materials. The relation between the phosphine cracker temperature and the cracking efficiency has been studied by mass spectroscopy during growth. The growth rate and morphology of the layers have been studied by varying the TMIn and phosphine flow rates as well as the substrate temperature. We have found that, under a wide range of growth conditions, the deposition rate is only determined by and proportional to the TMIn flow rate. This is in agreement with literature. Additionally, we observe that the growth rate decreases below a certain phosphine to TMIn flow rate (V/III) ratio and becomes phosphine flow limited. From investigations of the growth rate as a function of temperature, it is concluded that the desorption of indium species from InP starts at a temperature slightly below 540°C. For this desorption process, we have found an activation energy of (217 ± 20) kJ/mol. Further characterization of the InP layers has been carried out by photoluminescence and Hall measurements. From both methods, the optimum growth conditions have been established. Under these conditions, we reproduc-ibly obtain InP layers showing linewidths of the donor-bound exciton transition at 5K around 0.25 meV and a mobility at 77K of about 7.0·10⁴ cm²/Vs. From the analysis of the mobility in the temperature range from 20 to 300K, we conclude that, additionally to shallow donors and acceptors, deep-donor centers with an activation energy of about 150 meV are present in all layers.     

Sharp line emission spectra from GaAs FET like structures

Magneto-optical analysis of prominent photoluminescence lines from GaAs FET structures has been performed. Fifteen samples were investigated. Each consisted of a sulfur doped active layer on a high resistivity buffer layer (both epitaxially grown films) on a chromium doped GaAs substrate. The active layers were generally 2μm thick or less, except for two thicker layers (4 and 5μm) grown especially for this study. Buffer layer thicknesses ranged from 1.5 to 26μm. A model based on carrier diffusion through the active layer has been used to interpret the spectra as originating from the active-buffer interface region. All spectra contain strong-evidence of two donorbound exciton complexes associated with sulfur (1.51417eV) and silicon (1.51412eV). Other sharp spectral features included up to six lines associated with more complicated complexes. Linear Zeeman and quadratic diamagnetic behavior of the lines in applied magnetic fields are discussed. Supported under AF Contract F33615-77-C-5003 Supported under AF Contract F33615-76-C-1207     

Growth of Polarity-Controlled ZnO Films on (0001) Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The polarity control of ZnO films grown on (0001) Al₂O₃ substrates by plasma-assisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr₂O₃ layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I₈) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.     

Excitonic spectrum of the ZnO/ZnMgO quantum wells

Excitonic spectrum of the wurtzite ZnO/Zn_{1 ? x} Mg _x O quantum wells with a width on the order of or larger than the Bohr radius of the exciton has been studied; the quantum wells have been grown by the method of molecular beam epitaxy (with plasma-assisted activation of oxygen) on substrates of sapphire (0001). Low-temperature (25 K) spectra of photoluminescence excitation (PLE) have been experimentally measured, making it possible to resolve the peaks of exciton absorption in the quantum well. The spectrum of excitons in the quantum well is theoretically determined as a result of numerical solution of the Schrödinger equation by the variational method. The value of elastic stresses in the structure (used in calculations) has been determined from theoretical simulation of measured spectra of optical reflection. A comparison of experimental data with the results of calculations makes it possible to relate the observed features in the PLE spectra to excitons, including the lower level of dimensional quantization for electrons and two first levels of holes for the A and B valence bands of the wurtzite crystal. The values of the electron and hole masses in ZnO are refined, and the value of the built-in electric field introduced by spontaneous and piezoelectric polarizations is estimated.     

Characterization of closed space vapor transport GaP epitaxial layers

The growth of homoepitaxial GaP layers using Te-doped GaP as source material has been obtained by the so-called closed space vapor transport technique. The photoluminescence study shows that these layers, when grown under optimized thermodynamical conditions, have both a large luminescence efficiency and the same optical quality as the ones obtained by liquid phase epitaxy. The variation of the luminescence properties with the conditions of growth has been investigated. Both electron paramagnetic resonance and deep level transient spectroscopy detect the presence of deep levels that are not observed in liquid phase epitaxy materials.     

Interface structural defects and photoluminescence properties of epitaxial GaN and AlGaN/GaN layers grown on sapphire

Overall characterization of the GaN and AlGaN/GaN epitaxial layers by X-ray diffractometry and optical spectral analysis is carried out. The layers are grown by metalloorganic gas-phase epitaxy on (0001)-oriented single crystal sapphire wafers. The components of strains and the density of dislocations are determined. The effects of strains and dislocations on the photoluminescence intensity and spectra are studied. The results allow better understanding of the nature and mechanisms of the formation of defects in the epitaxial AlGaN/GaN heterostructures.     

Photoluminescence Characterization of Boron-doped Si Layers Grown by Molecular Beam Epitaxy

Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related photoluminescence spectra of molecular beam epitaxy Si layers annealed at 900 ℃ was studied with different doping concentrations and growth temperature. The broad photoluminescence band（from 0.75 eV to 0. 90 eV） including D1 and D2 bands was associated with high boron doping concentration in the samples, while D3 and D4 bands might be related to oxygen precipitates.     

MBE growth and Raman analysis of [hhk]GaAs/(Si or CaF2) highly strained hetero-structures

Highly strained GaAs layers have been grown by molecular beam epitaxy on (100)-, (111)- or (112)-oriented Si or CaF₂ substrates. The origin, sign, bisotropic nature, value, homogeneity and relaxation of the built-in strain have been studied by Raman spectroscopy. Specific measurements have been performed by using selection rules and line shape analysis over a wide temperature range.     

Self-Assembled CdTe Quantum Dots Grown on ZnTe/GaSb

We report the formation of CdTe self-assembled quantum dots (QDs) on high-quality ZnTe epilayers grown on a GaSb substrate by molecular-beam epitaxy. Reflection high-energy electron diffraction and atomic force micro- scopy measurements clearly show the formation of CdTe QDs. Photoluminescence (PL) measurements on ZnTe-capped CdTe QD samples show a wide distribution of dot size. The temperature dependence of PL spectra indicates much stronger exciton localization in QDs than that in quantum wells.     

High‐Quality Whispering‐Gallery‐Mode Lasing from Cesium Lead Halide Perovskite Nanoplatelets

Semiconductor micro/nano‐cavities with high quality factor (Q) and small modal volume provide critical platforms for exploring strong light‐matter interactions and quantum optics, enabling further development of coherent and quantum photonic devices. Constrained by exciton binding energy and thermal fluctuation, only a handful of wide‐band semiconductors such as ZnO and GaN have stable excitons at room temperature. Metal halide perovskite with cubic lattice and well‐controlled exciton may provide solutions. In this work, high‐quality single‐crystalline cesium lead halide CsPbX₃ (X = Cl, Br, I) whispering‐gallery‐mode (WGM) microcavities are synthesized by vapor‐phase van der Waals epitaxy method. The as‐grown perovskites show strong emission and stable exciton at room temperature over the whole visible spectra range. By varying the halide composition, multi‐color (400–700 nm).WGM excitonic lasing is achieved at room temperature with low threshold (~ 2.0 μJ cm^?2) and high spectra coherence (~0.14–0.15 nm). The results advocate the promise of inorganic perovskites towards development of optoelectronic devices and strong light‐matter coupling in quantum optics.