Recent research results on deep level defects in semi-insulating InP - Application to improve material quality

An apparent defect suppression effect has been observed in InP through an investigation of deep level defects in different semi-insulating (SI) InP materials. Quality improvement of SI-InP based on the defect suppression mechanism is presented.

Terahertz pulse generation with LT-GaAs photoconductive antenna

Low-temperature-grown GaAs (LT-GaAs) of 1-um thickness was grown at 250 degrees C on semi-insulating GaAs (001) substrate using EPI GEN-II solid-source MBE system. The sample was then in situ annealed for 10 min at 600 degrees C under As-rich condition. THz emitters were fabricated on this LTGaAs with three different photoconductive dipole antenna gaps of 1-mm, 3-mm, and 5-mm, respectively. The spectral bandwidth of 2.75 THz was obtaind with time domain spectroscopy. It is found that THz emission efficiency is increased with decreasing antenna gap. Two carrier lifetimes, 0.469 ps and 3.759 ps, were obtained with time-resolved transient reflection-type pump-probe spectroscopy.

Two-dimensional photonic crystals with a large photonic band gap designed by a rapid genetic algorithm

We used Plane Wave Expansion Method and a Rapid Genetic Algorithm to design two-dimensional photonic crystals with a large absolute band gap. A filling fraction controlling operator and Fourier transform data storage mechanism had been integrated into the genetic operators to get desired photonic crystals effectively and efficiently. Starting from randomly generated photonic crystals, the proposed RGA evolved toward the best objectives and yielded a square lattice photonic crystal with the band gap (defined as the gap to mid-gap ratio) as large as 13.25%. Furthermore, the evolutionary objective was modified and resulted in a satisfactory PC for better application to slab system.

Shallow donor defect formation and its influence on semi-insulating indium phosphide after high temperature annealing with long duration

Fe-doped semi-insulating (SI) InP has become semi-conducting (SC) material completely after annealing at 900 V for 10 hours. Defects in the SC and SI InP materials have been studied by deep level transient spectroscopy (DLTS) and thermally stimulated current spectroscopy (TSC) respectively. The DLTS only detected Fe acceptor related deep level defect with significant concentration, suggesting the formation of a high concentration of shallow donor in the SC-InP TSC results confirmed the nonexistence of deep level defects in the annealed SI-InP. The results demonstrate a significant influence of the thermally induced defects on the electrical properties of SI-InP. The formation mechanism and the nature of the shallow donor defect have been discussed based on the results.

Research on the band-gap of InN grown on siticon substrates

Photoluminescence (PL) and absorption experiments were carried out to examine the fundamental band-gap of InN films grown on silicon substrates. A strong PL peak at 0.78 eV was observed at room temperature, which is much lower than the commonly accepted value of 1.9 eV. The integrated PL intensity was found to depend linearly on the excitation laser intensity over a wide intensity range. These results strongly suggest that the observed PL is related to the emission of the fundamental inter-band transitions of InN rather than to deep defect or impurity levels. Due to the effect of band-filling with increasing free electron concentration, the absorption edge shifts to higher energy. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Growth and characterization of semi-insulating GaN films grown by MOCVD

High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arc-min, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 degrees C was measured to be approximate 10(9) and 10(6) Omega(.)cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.

Growth of high quality semi-insulating InP single crystal by suppression of compensation defects

Deep level defects in as-grown and annealed SI-InP samples were investigated by thermally stimulated current spectroscopy. Correlations between electrical property, compensation ratio, thermal stability and deep defect concentration in SI-InP were revealed. An optimized crystal growth condition for high quality SI-InP was demonstrated based on the experimental results.

Improvement of the electrical property of semi-insulating InP by suppression of compensation defects

Semi-insulating (SI) InP obtained by iron phosphide ambient annealing has very low concentration of deep level defects and better electrical property than SI-InP annealed in phosphorus ambient. The defect suppression phenomenon correlates with Fe diffusion and substitution in the annealing process. Analysis of the experimental result suggests that a high activation ratio of incorporated Fe in InP has an effect of defect suppression in Fe-doped and Fe-diffused SI-InP.

Selective and lithography-independent fabrication of 20 nm nano-gap electrodes and nano-channels for nanoelectrofluidics applications

A new method has been developed to selectively fabricate nano-gap electrodes and nano-channels by conventional lithography. Based on a sacrificial spacer process, we have successfully obtained sub-100-nm nano-gap electrodes and nano-channels and further reduced the dimensions to 20 nm by shrinking the sacrificial spacer size. Our method shows good selectivity between nano-gap electrodes and nano-channels due to different sacrificial spacer etch conditions. There is no length limit for the nano-gap electrode and the nano-channel. The method reported in this paper also allows for wafer scale fabrication, high throughput, low cost, and good compatibility with modern semiconductor technology.

GROWTH OF WIDE-BAND GAP IMMISCIBLE II-VI ALLOYS BY METALORGANIC VAPOR-PHASE EPITAXY

Although metalorganic vapor phase epitaxy (MOVPE) is generally regarded as a non-equillibrium process, it can be assumed that a chemical equilibrium is established at the vapor-solid interface in the diffusion limited region of growth rate. In this paper, an equilibrium model was proposed to calculate the relation between vapor and solid compositions for II-VI ternary alloys. Metastable alloys in the miscibility gap may not be obtained when the growth temperature is lower than the critical temperature of the system. The influence of growth temperature, reactor pressure, input VI/II ratio, and input composition of group VI reactants has been calculated for ZnSSe, ZnSeTe and ZnSTe. The results are compared with experimental data for the ZnSSe and ZnSTe systems.

NEW TYPE OF SILICON MATERIAL WITH VERY HIGH-QUALITY SURFACE-LAYER ON INSULATING DEFECT LAYER

A new-type silicon material, silicon on defect layer (SODL) was proved to have a very high quality surface microstructure which is necessary for commercially feasible high-density very large scale integrated circuits (VLSI). The structure of the SODL material was viewed by transmission electron microscopy. The SODL material was also proved to have a buried defect layer with an insulating resistivity of 5.7 x 10(10) OMEGA-cm.

AN ANALYSIS OF CHARGE STATES FOR LOCAL VIBRATIONAL-MODES BY OXYGEN DEFECTS IN SEMI-INSULATING GAAS

The high-resolution spectral measurements for new local vibrational modes near 714 cm-1 due to the oxygen defect in semi-insulating GaAs are analyzed on the basis of a model calculation by self-consistent bond orbital approach. Two charge states of oxygen atom with 1 and 2 extra electrons are assigned to be responsible for these local modes. The observed frequencies are explained by the properties of Ga-O-1 and Ga-O-2 bonds and the calculated cohesive energy indicates that the O-2 state is stable. The results are in good agreement with the kinetic analysis.

1ST-PRINCIPLES CALCULATIONS FOR QUASI-PARTICLE ENERGIES OF GAP AND GAAS

We have applied the Green-function method in the GW approximation to calculate quasiparticle energies for the semiconductors GaP and GaAs. Good agreement between the calculated excitation energies and the experimental results was achieved. We obtained calculated direct band gaps of GaP and GaAs of 2.93 and 1.42 eV, respectively, in comparison with the experimental values of 2.90 and 1.52 eV, respectively. An ab initio pseudopotential method has been used to generate basis wave functions and charge densities for calculating the dielectric matrix elements and self-enegies. To evaluate the dynamical effects of the screened interaction, the generalized-plasma-pole model has been utilized to extend the dielectric matrix elements from static results to finite frequencies. We presen the calculated quasiparticle energies at various high-symmetry points of the Brillouin zone and compare them with the experimental results and other calculations.