NEW FORMATION MECHANISM OF ELECTRIC-FIELD DOMAIN DUE TO GAMMA-X SEQUENTIAL TUNNELING IN GAAS/ALAS SUPERLATTICES

We have studied the sequential tunneling of doped weakly coupled GaAs/ALAs superlattices (SLs), whose ground state of the X valley in AlAS layers is designed to be located between the ground state (E(GAMMA1)) and the first excited state (E(GAMMA2)) of the GAMMA valley in GaAs wells. The experimental results demonstrate that the high electric field domain in these SLs is attributed to the GAMMA-X sequential tunneling instead of the usual sequential resonant tunneling between subbands in adjacent wells. Within this kind of high field domain, electrons from the ground state in the GaAs well tunnel to the ground state of the X valley in the nearest AlAs layer, then through very rapid real-space transfer relax from the X valley in the AlAs layer to the ground state of the GAMMA valley of the next GaAs well.

DETERMINATION OF THE CONDUCTION-BAND OFFSET OF A SINGLE ALGAAS BARRIER LAYER USING DEEP-LEVEL TRANSIENT SPECTROSCOPY

The tunneling from an AlGaAs confined thin layer to a GaAs layer in the GaAs/Al0.33Ga0.67As/GaAs structure during the trapped electron emission from deep level in the AlGaAs to its conduction band has been observed by deep level transient spectroscopy. With the aid of the tunneling effect, the conduction-band offset DELTAE(c) was determined to be 0.260 eV, corresponding to 63% of DELTAE(g). A calculation was also carried out based on this tunneling model by using the experimental value of DELTAE(c) = E2 - E1 = 0. 260 eV, and good agreement between the experimental and calculated curves is obtained.

HYDROGEN-RELATED DONOR IN SILICON-CRYSTALS GROWN IN A HYDROGEN ATMOSPHERE

Neutron transmutation doped (NTD) silicon crystals grown in a hydrogen atmosphere have been investigated by infrared absorption spectroscopy at a low temperature (10 K). An effective-mass-like donor state HD0/+ has been found at 110.8 me V below the conduction band bottom after rapid thermal annealing (RTA). The HD0/+ formation mechanism after NTD and RTA is briefly discussed, and tentatively attributed to H atoms present in the vicinity of some residual irradiation defects, like a complex of a H atom and a H-saturated vacancy.

TEMPERATURE-DEPENDENCE OF THE LOW-FIELD MOBILITY OF MINIBAND CONDUCTION IN SUPERLATTICES

The existing interpretation of the T-1 temperature dependence of the low-field miniband conduction is derived from certain concepts of conventional band theory for band structures resulting from spatial periodicities commensurable with the dimensionalities of the system. It is pointed out that such concepts do not apply to the case of miniband conduction, where we are dealing with band structures resulting from a one-dimensional periodicity in a three-dimensional system. It is shown that in the case of miniband conduction, the current carriers are distributed continuously over all energies in a sub-band, but only those with energies within the width of the miniband contribute to the current. The T-1 temperature dependence of the low-field mobility is due to the depletion of these current-carrying carriers with the rise of temperature.

SHEAR-DEFORMATION-POTENTIAL CONSTANT OF THE CONDUCTION-BAND MINIMA OF SI - EXPERIMENTAL-DETERMINATION BY THE DEEP-LEVEL CAPACITANCE TRANSIENT METHOD

The shear-deformation-potential constant XI-u of the conduction-band minima of Si has been measured by a method which we called deep-level capacitance transient under uniaxial stress. The uniaxial-stress (F) dependence of the electron emission rate e(n) from deep levels to the split conduction-band minima of Si has been analyzed. Theoretical curves are in good agreement with experimental data for the S0 and S+ deep levels in Si. The values of XI-u obtained by the method are 11.1 +/- 0.3 eV at 148.9 K and 11.3 +/- 0.3 eV at 223.6 K. The analysis and the XI-u values obtained are also valuable for symmetry determination of deep electron traps in Si.

DETERMINATION OF THE X-CONDUCTION-SUBBAND ENERGIES IN TYPE-II GAAS/ALAS/GAAS QUANTUM-WELL BY DEEP-LEVEL TRANSIENT SPECTROSCOPY

Using deep level transient spectroscopy (DLTS) the X conduction-subband energy levels in an AlAs well sandwiched by double GaAs layers were determined. Calculation gives eight subbands in the well with well width of 50 Angstrom. Among them, five levels and the other three remainders are determined by using the large longitudinal electron effective mass m(1)(1.1m(0)) and transverse electron effective mass m(t)(0.19m(0)) at X valley, respectively. Two subbands with the height energies were hardly detectable and the other six ones with lower energies are active in the present DLTS study. Because these six subbands are close to each other, we divided them into three groups. Experimentally, we observed three signals induced from the three groups. A good agreement between the calculation and experiment was obtained. (C) 1995 American Institute of Physics.

Mechanism of Wafer Bonding Process

国家自然科学基金

Yellow luminescence mechanism and persistent photoconductivity in n-GaN single crystal films grown on alpha-Al2O3(0001) substrates by LP-MOCVD

Unintentionally doped and Si-doped single crystal n-GaN films have been grown on alpha-Al2O3 (0001) substrates by LP-MOCVD. Room temperature photoluminescence measurement showed that besides the bandedges, the spectrum of an undoped sample was a broad deep-level emission band peaking from 2.19 to 2.30eV, whereas the spectrum for a Si-doped sample was composed of a dominant peak of 2.19eV and a shoulder of 2.32eV. At different temperatures, photoconductance buildup and its decay were also observed for both samples.. The likely origins of persistent photoconductivity and yellow luminescence, which might be associated with deep defects inclusive of either Ga vacancy(V-Ga)/Ga vacancy complex induced by impurities or N antisite (N-Ga), will be proposed.

Formation mechanism of defects in annealed InP

Dynamical formation mechanism of defects in the annealed nominally undoped semi-insulating InP obtained by high pressure, high temperature annealing of high purity materials is proposed. Local vibrational modes in tenths of InP samples reveal clearly existence of complexes related to hydrogen. Complexes of vacancy at indium site with one to four hydrogen atoms and isolated hydrogen or hydrogen dimers, complexes of hydrogen with various impurities are investigated by FTIR. Hydrogen can acts as an actuator for generation of antistructure defects. Fully hydrogenated indium vacancy dissociates leaving large lattice relaxation behind, deep donors, mainly larger complexes involving phosphorus at indium site and isolated hydrogen defects are created in nominally undoped InP after annealing. Also created are acceptor levels such as vacancy at indium site. Carrier charge compensation mechanism in nominally undoped InP upon annealing at high temperature is given. Microscopic models of hydrogen related defects are given. Structural, electronic and vibrational properties of LVMs related to hydrogen as well as their temperature effect are discussed.

Mechanism on exciton-mediated energy transfer in erbium-doped silicon

Exciton-mediated energy transfer model in Er-doped silicon was presented. The emission intensity is related to optically active Er concentration, lifetime of excited Er3+ ion and spontaneous emission. The thermal quenching of the Er luminescence in Si is caused by thermal ionization of Er-bound exciton complex and nonradiative energy back-transfer processes, which correspond to the activation energy of 6.6 and 47.4 meV, respectively. Er doping in silicon introduces donor states, a large enhancement in the electrical activation of Er (up to two orders of magnitude) is obtained by co-implanting Er with O. It appears that the donor states are the gateway to the optically active Er. (C) 2000 Elsevier Science B.V. All rights reserved.