Abstract: According to the Harrison’s model, the level change of conduction and valence bands caused by the strain of AlInGaAs/AlGaAs quantum well (QW) was analyzed firstly. The energy level of the electron and hole in the AlInGaAs/AlGaAs strained and GaAs/AlGaAs unstrained QW were calculated, respectively. In addition, taking the lorentzian function, the linear gain of the two QWs were calculated and discussed. Contrast the gain performance of GaAs/AlGaAs QW with that of AlyInxGa1-x-yAs/AlGaAs QW, it can be found that the strained AlyInxGa1-x-yAs/AlGaAs QW material has more promising optical gain than that of the GaAs/AlGaAs QW.
Abstract: Two chemical vapor transport methods with Zn(NH4)3Cl5 transport agent were developed to grow ZnSe bulk single crystals. Two kinds of Zn-rich ZnSe single crystals, conical crystal and flake crystal，were grown directly from untreated ZnSe polycrystals and two elements, respectively. The structure characters, purity and etch pit density were studied by rotating orientation XRD, PL spectrum and optical microscope. The contrastive investigation between two growth results indicated that the conical crystal was composed of (111) and (100) faces, and the flake crystal exhibited only (111) face. Moreover, the vicinal interface leaning to (111) face by the angle of 3.1° was the dominative growth face in vapor growth system, and growth occurs by layer-by-layer model. FWHM of RO-XRD pattern of ZnSe (111) face was 24sec for conical ZnSe crystal and 48s for ZnSe flake crystal. The results suggested that high-quality ZnSe crystals can be grown from the chemical vapor transport method with Zn(NH4)3Cl5 transport agent.
Abstract: The morphology evolution of ZnO films grown on sapphire (0001) by MOCVD have been studied as a function of buffer growth time and temperature by means of atomic-force microscope (AFM), x-ray diffractions (XRD) and optical microscopy. When the buffer growth temperature decreased to 450°C, the surface became smooth greatly, indicating the transition from typical 3D island growth to quasi-2D growth mode. As the buffer growth time exceeds 5min, the micron-sized pit-like features are formed. It is due to the lack of stabilization of adatoms under the “etching” action of ionized O2/Ar during high temperature buffer annealing
Abstract: The influence of Mg doping on structural and strain properties in GaN layers grown on sapphire substrates by metalorganic chemical vapor deposition was studied by means of high resolution X-ray diffraction and Raman scattering. The results showed that the disorder of GaN films aggravated and the quality reduced as Mg doping rate increasing. However, according to the theoretic calculation, the compressive stress determined by the Raman shift of the E2 mode was not due to the substitution of Mg atoms for Ga. Furthermore, the SEM measurements indicated that some Mg atoms substituted Ga to become acceptors, while most of them existed as Mg interstitials(Mgi) and aggregated at defects and dislocation, hence a great deal of cracks are introduced during decreasing temperature process for inhomogeneous strain distribution.
Abstract: Single phase of Ba1-xEuxMgAl10O17(0.02≤x≤0.14) phosphors were first successfully prepared by coprecipitation method at 1300°C, which is 300°C lower than the temperature of solid-state method. Different precipitants were used to evaluate the changes in the morphology and luminance properties. When using (NH4)2CO3 as precipitant, the phosphor particle without agglomeration has a more regular shape and uniform distribution. Their photoluminescence was
investigated under UV and VUV region, respectively. The emission spectrum excited by 254nm or 147nm showed a characteristic wide band with the peak at about 450nm. The synthesized phosphor showed much stronger emission intensity than that prepared by solid-state method, especially using (NH4)2CO3 as precipitant, it indicated that this novel process will be great potential in practical use.
Abstract: Recent strong demands for optoelectronic communication and portable telephones have encouraged engineers to develop optoelectronic devices, microwave devices, and high-speed devices using heterostructural compound semiconductors. Although the compound crystal growth techniques had reached at a level to control the compositional stoichiometry and crystal defects on a nearly atomic scale by the advanced techniques such as molecular beam epitaxy and metal organic chemical vapor deposition techniques, development of ohmic contact materials (which play a key role to inject external electric current from the metals to the semiconductors) was still on a trial-and-error basis. Our research efforts have been focused to develop, low resistance, refractory ohmic contact materials using the deposition and annealing techniques for n-GaAs, p-ZnSe, InP, p-SiC p-CdTe etc. It was found the growth of homo- or hetero–epitaxial intermediate semiconductor layers (ISL) was essential for low resistance contact formation. The importance of hetero-structural ISL was given taking an example of n-type ohmic contact for GaAs.
Abstract: We have investigated the magnetic properties and magnetostriction of ZnxNi1-xMnSb compounds prepared by solid state reaction method. It is found that for x less than 0.6 the magnetization of ZnxNi1-xMnSb almost remains unchanged. However, when x is larger than 0.6 the magnetization starts to drop linearly. Experimental result indicates that at low Zn concentrations, x < 0.7, the Curie temperature (TC) decreases with increasing Zn concentration x. However, when x > 0.7, the Curie temperature increases distinctly with increasing x. The Zn concentrartion dependence of magnetostrictive ceofficient is also studied. The experimental curve shows that when x < 0.6 the value of magnetostriction coefficient for ZnxNi1-xMnSb decreases linearly with the increasing Zn
concentration x. However, when x is above 0.6, the magnetostrictive ceofficient raises distinctly. By analyzing the XRD pattern, the structures of the materials are examined and the relationship between the properties and the structures are discussed. A structural phase transition is observed. It has been indicated that the structure plays an important role in the magnetic and magnetostrictive properties of the system.
Abstract: In order to understand carrier statistics in phosphorus-doped n-type diamond, electron statistics involving compensation and deep-dopant effect are theoretically analyzed. For n-diamond with a compensation ratio (c) larger than 1x10-4, the electron concentration (n) at room temperature (RT) is insensitive to the donor concentration (ND) and reduced with increasing the c value. On the other hand, for diamond with a c value smaller than 1x10-4, the n value at RT increases with increasing the ND value and is insensitive to the c value. Similarly, the length of Debye tailing (ln) at RT is reduced with increasing the c value for n-diamond with c>1x10-4 and is insensitive to the c value for n-diamond with c<1x10-4. However, it is found that an increase of temperature is effective to increase the n value and to reduce the ln value. The n value as large as 1015 cm-3 and the ln value as small as 100 nm are expected to be achieved at an elevated temperature of 473 K.
Abstract: This work demonstrates the condition optimization during liquid phase deposition (LPD) of SiO2/GaAs films. LPD method is further applied to form Al2O3 films on semiconductors with poison-free materials. Proceeding at room temperature with inexpensive equipment, LPD of silica and alumina films is potentially serviceable in microelectronics and related spheres.
Abstract: The quaternary HgCdZnTe (MCZT) epilayer was successfully grown on lattice matched Cd0.96Zn0.04Te/Si(111) substrates using isothermal vapor phase epitaxy (ISOVPE) method. It was found that Si wafer is an excellent barrier against Hg and Cd diffusion. Cross-sectional images reveal a flat and well-distinguished interface between MCZT and Si, and voids formed due to interdiffusion was not observed in MCZT layer above the Si wafer. It was demonstrated that it was possible to yield an almost homogeneous MCZT epilayer without compositional gradient by selecting suitable growth time.