WELL WIDTH DEPENDENCE OF THE EXCITON LIFETIME IN NARROW GAAS/GAALAS QUANTUM-WELLS

We have studied the radiative excitonic lifetime as a function of the well width in GaAs/GaAlAs quantum wells. An increasing lifetime with decreasing well width has been observed in very narrow and high quality GaAs/GaAlAs quantum wells, and attributed to the reduced overlap of the electron and hole wave functions and the increase of the exciton effective volume. This is the first observation of its kind in the conventional GaAs/GaAlAs quantum wells.

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.

FIELD-EFFECT ON THERMAL EMISSION FROM THE 0.40 EV ELECTRON LEVEL IN INGAP

Results are reported of electric-field dependence on thermal emission of electrons from the 0.40 eV level at various temperatures in InGaP by means of deep-level transient spectroscopy. The data are analyzed according to the Poole-Frankel emission from the potentials which are assumed to be Coulombic, square well, and Gaussian, respectively. The emission mte from this level is strongly field dependent. It is found that the Gaussian potential model is more reasonable to describe the phosphorus-vacancy-induced potential in InGaP than the Coulombic and square-well ones.

ENERGY-LEVEL CALCULATIONS OF THE RECONSTRUCTED 90-DEGREES PARTIAL DISLOCATION IN SILICON

An LCAO scheme taking into account 10 atomic orbitals (s-, p-, and d-type) applied to a supercell containing 256 atoms is used to calculate the bound states of the reconstructed 90-degrees partial dislocation in Si. The results differ significantly from our earlier calculations on the unreconstructed 90-degrees partial using the same method. We find two bands separate from each other in the entire Brillouin zone and the upper band penetrates deep into the indirect band gap which is in contradiction with the general opinion that core reconstruction clears the band gap of dislocation states.

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.

DISORDER POINT FOR 2D ELECTRONS IN A HALF-FILLED LANDAU-LEVEL

Short-range correlations of two-dimensional electrons in a strong magnetic field are shown to be triangular in nature well below half-filling, but honeycomb well above half-filling. The half-filling point is thus proposed, and qualitatively confirmed by three-body correlation calculations, to be a new type of disorder point where short-range correlations change character. A wavefunction study also suggests that nodes become unbound at half-filling. Evidence for incompressibility but deformability of the half-filling state earlier suggested by Fano, Ortolani and Tosatti, is also presented and found to be in agreement with recent experiments.

Reflectance-difference spectroscopy study of the Fermi-level position of low-temperature-grown GaAs

The results of a reflectance-difference spectroscopy study of GaAs grown on (100) GaAs substrates by low-temperature molecular-beam epitaxy (LT-GaAs) are presented. In-plane optical anisotropy resonances which come from the linear electro-optic effect produced by the surface electric field are observed. The RDS line shape of the resonances clearly shows that the depletion region of LT-GaAs is indeed extremely narrow (much less than 200 Angstrom). The surface potential is obtained from the RDS resonance amplitude without the knowledge of space-charge density. The change of the surface potential with post-growth annealing temperatures reflects a complicated movement of the Fermi level in LT-GaAs. The Fermi level still moves for samples annealed at above 600 degrees C, instead of being pinned to the As precipitates. This behavior can be explained by the dynamic properties of defects in the annealing process.

Characterization of recombination centres in n-type Hg1-xCdxTe

The defect levels in Hg1-xCdxTe P+N junction photodiodes (x = 0.4) were first studied using deep-level transient spectroscopy. Two electron traps, E(1)(0.06) and E(2)(0.15), and two hole traps, H-1(0.075) and H-2(0.29), were obtained, Characteristic parameters-the minority lifetime of the devices and the dynamic resistance-area product at zero bias-are estimated according to these levels. Results show that these two minority levels may be important in controlling lifetime. We have studied the recombination mechanism of the hole trap H-2(0.29) further. It has a large activation energy and satisfies the formula sigma(T) = sigma(x) exp(-E(F)/E(T)). This reflects the fact that its recombination mechanism is multiphonon nonradiative recombination, which is rarely reported in narrow-bandgap materials.

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.