PHOTOLUMINESCENCE SPECTRA OF STRAINED HETEROSTRUCTURE OF INP ON GAAS SUBSTRATE GROWN BY METAL-ORGANIC CHEMICAL VAPOR-DEPOSITION

A high-energy shift of the band-band recombination has been observed in photoluminescence spectra of the strained InP layer grown on GaAs substrate. The InP layer is under biaxial compressive strain at temperatures below the growth temperature, because the thermal expansion coefficient of InP is smaller than that of GaAs. The strain value determined by the energy shift of the band-edge peak is in good agreement with the calculated thermal strain. A band to carbon acceptor recombination is also identified.

METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION GROWTH OF GAN

Single-crystal GaN films have been deposited on (01 (1) over bar 2) sapphire substrates using trimethylgallium (TMGa) and NH3 as sources. The morphological, crystalline, electrical and optical characterizations of GaN film are investigated. The carrier concentration ofundoped GaN increases with decreasing input NH3-to-TMGa molar flow ratio.

Low-Temperature Growth of ZnO Films on GaAs by Metal Organic Chemical Vapor Deposition

ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precursor, respectively. The effects of the growth temperatures on the growth characteristics and optical properties of ZnO films were investigated. The X-ray diffraction measurement （XRD） results indicated that all the thin films were grown with highly c- axis orientation. The surface morphologies and crystal properties of the films were critically dependent on the growth temperatures. Although there was no evidence of epitaxial growth, the scanning electron microscopy （SEM） image of ZnO film grown at 400℃ revealed the presence of ZnO microcrystallines with closed packed hexagon structure. The photoluminescence spectrum at room temperature showed only bright band-edge （3. 33eV） emissions with little or no deep-level e- mission related to defects.

Zn-doped InGaAs Base Heterojunction Bipolar Transistors Grown by Low Pressure Metal Organic Chemical Vapor Deposition

High performance InP/InGaAs heterojunction bipolar transistors(HBTs) have been widely used in high-speed electronic devices and optoelectronic integrated circuits. InP-based HBTs were fabricated by low pressure metal organic chemical vapor deposition(MOCVD) and wet chemical etching. The sub-collector and collector were grown at 655 ℃ and other layers at 550 ℃. To suppress the Zn out-diffusion in HBT, base layer was grown with a 16-minute growth interruption. Fabricated HBTs with emitter size of 2.5×20 μm~2 showed current gain of 70~90, breakdown voltage(BV_(CE0))>2 V, cut-off frequency(f_T) of 60 GHz and the maximum relaxation frequency(f_(MAX)) of 70 GHz.

Metal-organic Vapor Phase Epitaxy Growth and Characterization of InAlGaN Epilayers

In order to improve crystal quality for growth of quaternary InAlGaN, a series of InAlGaN films were grown on GaN buffer layer under different growth temperatures and carrier gases by low-pressure metal-organic vapor phase epitaxy. Energy dispersive spectroscopy (EDS) was employed to measure the chemical composition of the quaternary, high resolution X-ray diffraction (HRXRD) and photoluminescence (PL) technique were used to characterize structural and optical properties of the epilayers, respectively. The PL spectra of InAlGaN show with and without the broad-deep level emission when only N2 and a N2+H2 mixture were used as carrier gas, respectively. At pressure of 1.01×104 Pa and with mixed gases of nitrogen and hydrogen as carrier gas, different alloy compositions of the films were obtained by changing the growth temperature while keeping the fluxes of precursors of indium (In), aluminum (Al), gallium (Ga) and nitrogen (N2) constant. A combination of HRXRD and PL measurements enable us to explore the relative optimum growth parameters-growth temperature between 850℃ and 870℃,using mixed gas of N2+H2 as carrier gas.

Behavior of Pentacene Initial Nucleation on Various Dielectrics and Its Effect on Carrier Transport in Organic Field-Effect Transistor

The influence of dielectric surface energy on the initial nucleation and the growth of pentacene films as well as the electrical properties of the pentacene-based field-effect transistors are investigated. We have examined a range of organic and inorganic dielectrics with different surface energies, such as polycarbonate/SiO2, polystyrene/SiO2, and PMMA/SiO2 bi-layered dielectrics and also the bare SiO2 dielectric. Atomic force microscopy measurements of sub-monolayer and thick pentacene films indicated that the growth of pentacene film was in Stranski-Kranstanow growth mode on all the dielectrics. However, the initial nucleation density and the size of the first-layered pentacene islands deposited on different dielectrics are drastically influenced by the dielectric surface energy. With the increasing of the surface energy, the nucleation density increased and thus the average size of pentacene islands for the first mono-layer deposition decreased. The performance of fabricated pentacene-based thin film transistors was found to be highly related to nucleation density and the island size of deposited Pentacene film, and it had no relationship to the final particle size of the thick pentacene film. The field effect mobility of the thin film transistor could be achieved as high as 1.38 cm(2)/Vs with on/off ratio over 3 x 10(7) on the PS/SiO2 where the lowest surface energy existed among all the dielectrics. For comparison, the values of mobility and on/off ratio were 0.42 cm(2)/Vs and 1 x 10(6) for thin film transistor deposited directly on bare SiO2 having the highest surface energy.

Broadband short-range surface plasmon structures for absorption enhancement in organic photovoltaics

We theoretically demonstrate a polarization-independent nanopatterned ultra-thin metallic structure supporting short-range surface plasmon polariton (SRSPP) modes to improve the performance of organic solar cells. The physical mechanism and the mode distribution of the SRSPP excited in the cell device were analyzed, and reveal that the SRSPP-assisted broadband absorption enhancement peak could be tuned by tailoring the parameters of the nanopatterned metallic structure. Three-dimensional finite-difference time domain calculations show that this plasmonic structure can enhance the optical absorption of polymer-based photovoltaics by 39% to 112%, depending on the nature of the active layer (corresponding to an enhancement in short-circuit current density by 47% to 130%). These results are promising for the design of organic photovoltaics with enhanced performance.