We describe the fabrication, characterization and frequency doubling properties of first order stacks of diffusion bonded 2″ diameter GaAs wafers. Near IR imaging through the stacks indicated that excellent bonding was obtained over 40%–70% of the central area of the wafers. A power spectrum analysis of the spectral noise (due to interface reflections) appearing in the transmission data is shown to be a quantitative diagnostic tool useful for determining interface quality and for accurately estimating the thickness of the bonded layers in a stack. The conversion efficiency for a four layer stack at 10.6 microns was found to be 0.03% or 3 mJ for a 10 mJ pulse with a 100 nanosecond pulse length. The corresponding efficiency for cw SHG was found to be 0.0002%.

Thermal Admittance Spectroscopy(TAS) has been used to detect energy levels in the bandgap of CdGeAs2 specimens. Capacitance-Voltage(CV) measurements were used to determine the net free carrier concentration of the specimens as well as the conductivity type. All specimens were found to be p-type. CV measurements determined that the free carrier densities ranged from 1.2 × 1017 cm−3 to 8 × 1018 cm−3. Usually one peak (but in some cases two) was observed in the thermal admittance spectra. One peak present in two samples indicates an acceptor with a thermal activation energy of Ev+(0.10–0.13) eV which corresponds closely to the value of 0.10–0.12 eV found from Hall effect measurements on these specimens. The additional peak observed could correspond to a second deeper acceptor at Ev+0.346 eV, however, the energy could not be accurately determined because the peak was not fully resolved. Evidence for the existence of two native acceptors from electron paramagnetic resonance has recently been reported which tends to support a two acceptor model.

Selenium disulfide has been demonstrated to be an effective passivant for GaAs (001) surfaces. This chemical treatment can be more robust and effective in reducing surface-states-based Fermi level pinning than other analogous chemical treatments. We have studied SeS2-passivated surfaces, formed by treatment of GaAs in SeS2:CS2 solution, with synchrotron radiation photoemission spectroscopy. The SeS2-treated surface consists of a chemically stratified structure of several atomic layers thickness. The As-based sulfides and selenides appear to reside on the outermost surface with the Ga-based compounds adjacent to the bulk GaAs substrate. The motion of the Fermi level within the band gap was monitored during controlled annealing conditions allowing for the specific chemical moieties responsible for the reduction in surface charge to be identified. As-based species are removed at low annealing conditions with little motion of the Fermi level. GaSe-based species, formed on the surface, are clearly shown to be associated with the unpinning of the Fermi level.

Erbium (Er) was co-implanted with ( i ) nitrogen (N), ( ii) oxygen (0) and (iii) N and 0 into Al0.7Ga0.3As substrates. Compared with the Al0.7Ga0.3As:Er sample, the 20 K Er3+ -related 1.54 μm integrated photoluminescence (PL) intensity from the Al0 7Ga0.3As:Er,N and Al0.7Ga0.3As:Er,N,O samples were enhanced approximately fifteen and ten times more, respectively. Thermal quenching of Er3+-related emission from Al0.7Ga0.3As:Er,N,O was smaller than that of Er3+-related emission from Al0.7.Ga0.3As-Er,N The 20 K Er3+-related 0.98 μm PL which was radiated by transition from the second excited state (4I1/2) to the ground state (4I1/2) was observed. The 0.98 μm PL intensity from Al0.7Ga0.3As:Er,N,O generally decreased with increasing 0 dosage from 1 × 1013 cm−2 to 1 × 1015 cm−2. These results suggest the formation of different complexes composed of Er and the impurities (N,O). This leads to the generation of complex related traps in the band-gap of Al0.7Ga0.3As as a result of the co-implantation of the impurities. It was found that the trap level of the Er-N complex center lay between 2.05 eV and 1.26 eV, and that of the Er-N-O complex center lay between 1.26 eV and 0.82 eV.

The effect of the secondary light illumination of hv = 0.9 eV on the photoquenched and the enhanced states in semi-insulating GaAs are investigated by using piezoelectric photoacoustic (PPA) measurements at 80 K. It is found that the secondary light causes an optical recovery from EL2* to EL2° and this is in agrezment with the result reported by using infrared optical absorption measurements. We observed a broad peak around 0.9 eV after the secondary light illumination for the first time. The most important finding is that the PPA spectra after the secondary light illumination on the quenched and the enhanced states are the same in the whole photon energy region. We concluded that the secondary light of hv = 0.9 eV induces both an optical recovery and generation of metastable state of the EL6 level. The difference of the transformation rates of these two processes explains well the observed complex natures of the PPA signal under the secondary light illumination.

We report on the evidence of photo-assisted resonant tunneling through localized states in AlAs/GaAs double-barrier structures (DBSs) with undoped GaAs spacers. In the photocurrent measurement, additional peaks were observed at voltages lower than that of resonance and were enhanced with the laser power. This behavior was more pronounced as the thickness of spacer layers in the DBS increased. These results are attributed to the resonant tunneling of electrons through the localized states, they are induced in the neighboring barriers, by the photoexcited carriers in spacers. We discuss the localization effect of photoexcited carriers on the resonant tunneling.

Oxygen related defects in Al-containing semiconductors have been determined to degrade luminescence efficiency and reduce free carrier lifetime, affecting the performance of light emitting diodes and laser diodes. We have used the oxygen doping source, diethylaluminum ethoxide, (C2H5)2A1OC2H5, to intentionally incorporate oxygen-related defects during growth of In0.5(AlxGa1−x)0.5P by Metalorganic Vapor Phase Epitaxy (MOVPE). Our investigations have identified several defects which are ‘intrinsic’ or present in non-intentionally oxygen-doped n-type In0.5(AlxGa1−x)0.5P as well as those due to oxygen, which introduces defect states near the middle of the conduction band. Deep level transient spectroscopy and photoluminescence data obtained for these defects over a range of composition, are presented illustrating the trends in defect structure with alloy composition. The impact of oxygen contamination on the visible emission spectrum is presented and discussed in terms of the defect structure.

Dislocations and traps in MBE grown p-InGaAs/GaAs lattice-mismatched heterostructures are investigated by Cross-section Transmission Electron Microscopy (XTEM), Deep Level Transient Spectroscopy (DLTS) and Photo-luminescence (PL). The misfit dislocations and the threading dislocations observed by XTEM in different samples with different In mole fractions and different InGaAs layer thickness generally satisfy the Dodson-Tsao's plastic flow critical layer thickness curve. The threading dislocations in bulk layers introduce three hole trap levels HI, H2 and H5 with DLTS activation energies of 0.32 eV, 0.40 eV, 0.88 eV, respectively, and one electron trap El with DLTS activation energy of 0.54 eV. The misfit dislocations in relaxed InGaAs/GaAs interface induce a hole trap level H4 with DLTS activation energy between the range of 0.67–0.73 eV. All dislocation induced traps are nonradiative recombination centers which greatly degrade the optical property of the InGaAs/GaAs layers.

The homogeneity of semiinsulating Fe-doped InP wafers is studied using mapping techniques, Scanning Photocurrent (SPC) and Scanning Photoluminescence (SPL). These techniques allow to map with a micrometric spatial resolution the distribution of electrically active levels, in particular substitutional iron levels, Fe2+ and Fe3+. The correlation between both measurements allows to obtain information about the local compensation in terms of the [Fe3++Fe2+]/[Fe2+] ratio. Samples thermally treated were studied in order to analyse the consequences of the annealing on the homogeneity.

InxGa1−xAs structures with compositionally graded buffers were grown with organometallic vapor phase epitaxy (OMVPE) on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy (PV-TEM and X-TEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in In.Gal.,As. The strain fields from misfit dislocations induce this phase separation in the <110> directions. At growth temperatures above and below this temperature, the surface roughness decreases significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−x,As determined to be 700 °C, it was possible to produce In0.33Ga0.67As diodes on GaAs with threading dislocation densities < 8.5 × 106/cm2.

Intersubband transitions in n-type InGaAs/AlGaAs multiple quantum wells were studied as a function of 1.0 to 5.0 MRad γ-ray irradiation dose using the optical absorption technique. The spectra were recorded at both 295 and 77K. The results show that the total integrated area of the intersubband transition is decreased as the irradiation dose is increased. This could be explained as follows: The secondary electrons generated from the γ-ray irradiation cause lattice damages where traps and point defects are created. Some of the electrons in the quantum wells are trapped by these defects causing the two dimensional electron gas (2DEG) density to decrease. The reduction of the 2DEG density thus leads to the reduction of the total integrated area of the intersubband transitions.

In this study, we demonstrate the growth of highly compressively strained InGaAs/JnGaAsP quantum well structures with large well thiclmess by low pressure metalorganic chemical vapor deposition for extending the emission wavelength of lasers. By comparing the photolumineswnce characteristics of quantum wells grown at different temperatures, it is clarified that a relatively high quality quantum well layer emittig at 2.0 μ, can be obtained at a growth temperature of 650°C. 1.95-μm-wavelength InGaAs/InGaAsP highly compressively strained quantum well DFB laser for laser spectroscopy monitors was also fabricated. Double quantum-well DFB laser operating at 1.95 μm exhibits threshold currents as low as 6 mA and 6.2 mW maximum output powers. 2.04-μm-wavelength DFB laser is also described.

Vertical cavity surface emitting laser (VCSEL) structure designed at 1.55 μm was grown by low pressure metalorganic chemical vapor deposition method. The VCSEL structure contains top and bottom distributed Bragg reflector (DBR) and single cavity active layer. The DBR was grown with In0.53Al0.14Ga0.33As and In0.52Al0.48As quarter lambda wavelength layer, alternatively. The growth temperature was as high as 750°C to prevent ordering and phase separation of the In0 52Al0.48As layer. The In0.52Al0.48As buffer layer was subsequently grown on the InP buffer layer in order to make an abrupt uniform interface. Unity reflectance was achieved at the center of 1.55 μm with 35.5 pairs undoped DBR layer. The reflectance spectrum of undoped DBR showed a wide flat-band region (greater than 50 nm) where the reflectivity was more than 99.5 %. The center wavelength of DBR was previously determined by an in-situ laser reflectometry technique during the growth of the whole structure. An infrared laser operating at 1.53 μm, which was the design wavelength of DBR layer was used as an in-situ measuring tool. The In0.53Ga0.47As multiple quantum well was used as a cavity layer. The reflectance spectrum of VCSEL structure, which included a single cavity active layer, showed excellent square shaped stop band and also showed an absorption region at the center of the flat band.

We have studied the effect of geometric factors on the polarization properties of verticalcavity surface-emitting lasers with tilted pillar structures. Laser pillars with circular, square, diamond, and rectangular shapes were formed using reactive ion beam etching, by tilting the substrate with an angle of 15° ∼ 30° toward the [110] or [110] direction. We measured the polarization characteristics for the devices of 10 ∼ 20 atm size. We observed that an effective geometric factor on the polarization selectivity in tilted pillar structures is an asymmetric shape of vertical-cavity rather than an anisotropic shape of device area in planar direction.

CaF2 layers were grown by molecular beam epitaxy on differently prepared Si(111) substrates. X-ray reflectivity spectra were measured and fitted. From the fitting process, the thickness of the CaF2 layer was precisely (within 1 Å) determined and the CaF2/Si interface roughness was also obtained. This roughness was used as an evaluation parameter for the quality of the layers. The CaF2/Si sample from which the intentional oxide was desorpted at 800°C inside the growth chamber exhibited the most clear x-ray reflectivity spectrum with very well resolved interference fringes. The epitaxial relations of the CaF2/Si samples grown at temperatures between 250 and 700°C were determined from x-ray diffraction analysis.

The theory of optical absorption due to interband transitions in direct-gap semiconductors is revisited. A new analytical expression for linear absorption coefficient in narrow-gap semiconductors is obtained by including the nonparabolic band structure due to Keldysh and Burstein-Moss shift. Numerical results are obtained for Hg1−xCdxTe for several values of x and temperature, and compared with recent experimental data. The agreement is found to be good.

In this paper, we have investigated the Burstein-Moss shift(BMS) in QDs of III-V, II-VI and IV-VI semiconductors in the presence of a parallel magnetic field on the basis of newly formulated carrier disperson laws. It is found, taking QDs of InSb, Cds and CdTe as examples that the BMS increases with increasing doping and decreasing film thickness in ladder like manners. The numerical values of the BMS in QDs are much greater than that of their corresponding values for bulk specimens. The theoretical results as presented here are in agreement with the experimental observations as reported in literature.

In this paper we have studied the Burstein-Moss shift in quantum wires and dots of ternary and quaternary materials on the basis of a newly formulated electron dispersion law which occurs as a consequence of heavy doping. It is found taking Hg1−xCdxTe and In1−xGaxAsyP1−y lattice matched to InP as examples that the Burstein-Moss shift exhibits oscillatory dependences for quantum wires and dots of the said materials with respect to doping and film thickness respectively. Besides, the numerical values of the same shift is greatest in quantum dots and least in quantum wires. In addition, the theroretical analysis is in agreement with the experimental datas as given elsewhere.