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Gamma-phase lithium aluminate (LiAlO2) single crystal is grown by Czochralski pulling method and a-plane LiAlO2(LAO) is chosen as the substrate for subsequent gallium nitride (GaN) epitaxial growth by plasma-assisted molecular beam epitaxy (PAMBE). The lattice mismatch between the nitride and the substrate is greatly reduced due to small lattice mismatch of~0.3% between [0001]GaN and [010]LAO and of~1.7% between [11-20]GaN and [001]LAO in the plane of the substrate LAO(100). Pure hexagonal [10-10]GaN is successfully grown directly on the LAO substrate without buffer layer. Crystal quality and properties are analyzed through a series of measurements, including reflection high-energy electron diffraction (RHEED), field-emission electron microscopy (FESEM), electron backscatter diffraction (EBSD), x-ray diffraction and cathodo luminescence (CL).

Over the last few years‚ the number of subscribers of wireless services has increased at an explosive rate. This ever growing demand for wireless communications services is constantly increasing the need for better coverage‚ improved capacity and higher quality service. Smart antennas system is an effective technology for the performance improvement of wireless communications. Switching-beam smart antennas use a number of fixed beams at an antenna site. The system provides a beam that offers the best signal enhancement and interference reduction. Using the approach of dynamic switching-beam antenna system‚ an intelligent sector beam synthesis of adjustable sector width can be established. By doing so‚ traffic load balancing can be achieved, and therefore, system capacity is increased. In this thesis, a beam-pattern synthesis algorithm proposed by M.H. Er is applied to shape array patterns with an adjustable mainlobe width and average sidelobe level reduction. Using an established database of weighting for circular arrays, the proposed smart antennas can adjust suitable sectors for the high dense subscribers not uniformly distributed. Simulation results demonstrate the proposed technique can dramatically improve the performance of traditional switching-beam antennas.

The relation between the electrical property and the material microstructure of InSb grown on Si utilizing electron beam evaporation technology has been investigated. The improvement of the InSb electrical property with controlling annealing environment after post annealing is demonstrated. The crystal structure of InSb thin films were characterized with X-ray diffraction (XRD) and the surface morphology was examined by scanning electron microscope (SEM). The composition of InSb films was analyzed by electron probe microscope analysis (EPMA) and the mobility of InSb films were measured by Hall measurement. Finally, the grain size and texture of InSb films microstructure were studied by transmission electron microscope (TEM). The films were grown with different In/Sb flux ratio by controlling electron energy during electron evaporation. The results show that the poly-InSb films were formed due to large lattice difference between Si and InSb . The InSb films which had higher In concentration behave higher mobility. The highest mobility of the as-grown film is around 12000(cm2/Vs). The mobility of InSb can be improved to 26000 (cm2/Vs) by added extra Sb source annealed at 500¢J for 5 hours in an sealed ampoule. The extra Sb which dissolved with the existed In droplet in the film and adjust the composition ratio of In/Sb closing to 1:1. Besides, the post-annealing process provides the InSb film to gain much better texture. Both these two factors contribute to improve the electrical property of InSb films.

This work is to control the fluxes of the Ga, In and Al sources in our MBE system to grow lattice-matched InGaAs, InAlAs and InGaAlAs epi-layers on InP substrates. With the As overpressure condition in the MBE system, we can control the temperature of Ga K-cell to modulate the flux of Ga. In ideal situation, the flux of Ga has a direct ratio with the GaAs growth rate on GaAs substrate, so we can find the Ga flux dependence on temperature by measuring the RHEED oscillation frequency. From the growth rate data of InGaAs on GaAs substrate at lower In composition, the In flux was obtained by comparing the growth rate ratio to the GaAs case. In the same way, we can also get the flux of Al by the growth of AlAs or AlGaAs on GaAs substrate. With the results of flux experiment, we can modulate the temperature of Ga, In and Al K-cells to compose InGaAs, InAlAs and InGaAlAs lattice-matched on InP substrates. The epi-layer quality was examined by X-ray diffraction and photo-absorption spectrum. We have built the flux equations for the Ga, In and Al sources from the experiment data. With the In K-cell temperature at 833~836¢J, Ga(1) at 931¢J and Al at 1094¢J, we have grown ternary compound semiconductors of In0.532Ga0.468As and In0.523Al0.477As lattice-matched on InP substrates. When the In K-cell temperature at 833~836¢J, Ga(2) at 912¢J and Al at 1059¢J, a quaternary compound semiconductor of In0.527Ga0.245Al0.228As (Eg=1eV) lattice-matched on InP substrate was demonstrated.

Abract This paper concems studies of CIS solar cell based on ZnSe an ZnSeTe window layer. ZnSe an ZnSeTe films are grown by Molecular Beam Deposition (MBD).This research is important for several reasons : (1)Development of non-cadmium buffer layer may be essential for CIS solar cells to be accepted in the marketplace ; (2)Development of direct ZnO/CIS cells could lead to a simplified cell (3)knowledge gained in investigations of ZnO and ZnSeTe buffer layer may help us understand the unique role CdS plays in CdS/CIS solar cell .

The work of this thesis includes the growth of TE polarization and polarization insensitive semiconductor optical amplifier structures by molecular beam epitaxy. The former is suited to fabricate the SOA and laser of the emitter, the latter is suited to fabricate the SOA of the repeater and receiver. The materials of InAl(1)As, InGa(1)Al(2)As and InGa(2)As were used to be the cladding layer, SCH layer and quantum well(QW), respectively. The first kind of our SOA structures is for 1.55-£gm TE polarization. The materials of InGa(1)As and InGa(2)As were used to be QW and sub-well, respectively. The second kind of our SOA structures is for 1.55-£gm polarization insensitive. To get polarization insensitive characteristics we use tensile strained InGa(3)As material and add two very thin compressive strain layers, InGa(1)As, in QWs to be sub-wells to mostly confine hh1 state. It has the effect of reducing red shift on the e1-hh1 transition and help to partially balance the strain in QW before the thickness of the tensile strained InGa(3)As exceeds one half of the critical layer thickness. These two kinds of structures include three QWs with modulation doping. It can reduce transparency current and noise figure and increase the saturation output power of SOA with the n-type modulation doping. We had successfully grown the polarization insensitive SOA structure for 1.52-£gm. The wavelength of TE polarization SOA structures we grew were at 1.45(µm) and 1.47(µm) and there were somewhat differences between the designed and grown. We can increase the PL efficiency after rapid thermal annealing at 550¢J for 30(s)~45(s).

The work of this thesis includes designs, molecular beam epitaxy (MBE) growths and optical study of electro-absorption modulator (EAM) structures. Three EAM structures are designed near 1.5 um : symmetric, asymmetric multiple quantum wells (MQWs) of TE polarization, and polarization insensitive MQWs. For symmetric and asymmetric MQWs simulation of TE polarization, their red-shift are 31 nm and 50 nm, respectively, as the electric field decrease from -40 kV/cm to -120 kV/cm. For polarization insensitive MQWs, we use the strained quantum-well concept to achieve same transition energy and absorption. After growth by MBE system, the samples were fabricated in mesa type by photolithography and wet etching. For symmetric and asymmetric quantum wells of TE polarization¡Gthe red-shift are 16 nm and 49 nm, respectively, as the bias decrease form 0-1 volt to 0-6 volt. Because of small ¡µn near subband transition energy, these two samples exhibit small chirp parameter. However, the photoluminescence (PL) and photocurrent spectra of these two ones were not near 1.5 um and obvious absorption edge. The possible reason is that the molecular beam flux have changed during growth. For polarization insensitive MQWs, the PL spectra shows 1494 nm, which only 25.6 nm differ from our design. Also, the photocurrent spectra of TE and TM polarization nearly exhibit same transition energy and have small chirp parameter.