摘要:

Large, rapid light induced changes are reported for photoconductivities, electron mobility‐lifetime products, and forward bias currents in hydrogenated amorphous silicon (a‐Si:H) films and Schottky barrier cell structures. The absence of concurrent changes in subgap absorption and quantum efficiencies are clearly inconsistent with the widely held view that the kinetics of degradation ina‐Si:H materials and cells can be quantified solely in terms of neutral dangling bond defects. The self‐consistent analysis of all the results was carried out for films and Schottky barrier structures by including charged defects and using a three‐Gaussian distribution of donorlike and acceptorlike defect states. Such self‐consistent development of ‘‘operational’’ parameters for these gap states offers a method for reliable and quantitative correlations between solar cell performance and stability with the properties of their bulk materials. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117198

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The carrier relaxation kinetics and nonlinear optical properties of strain‐induced laterally ordered (InP)2/(GaP)2quantum wire (QWR) samples were examined with time‐resolved cathodoluminescence. A temperature dependence of the QWR luminescence decay time reveals that thermal activation of carriers in the QWR and transfer to and from In0.49Ga0.51P barriers plays an important role in determining the measured lifetimes. The presence of disorder in the QWRs was found to induce inhomogeneous regions which exhibit large variations in carrier capture and band filling. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117199

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Polycrystalline silicon on glass substrates was grown by a method based on the creation of nucleation sites using laser crystallization of amorphous silicon followed by thermal annealing at temperatures below 600 °C. Annealing induces the crystallization of the material around the seeds, eventually leading to coalescence of adjacent domains before spontaneous nucleation sets in. Micro‐Raman spectroscopy shows that the seeds experience a tensile stress, which causes a radial birefringence in the surrounding amorphous silicon, detected by optical anisotropy measurements. We conjecture that this stress facilitates the crystallization of the material around the seed upon thermal annealing. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117200

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A large photocurrent multiplication reaching 130 000‐fold at room temperature has been observed in naphthalene tetracarboxylic anhydride (NTCDA) film sandwiched between metal electrodes. This phenomenon is reasonably interpreted in terms of the tunneling injection of electrons from a metal electrode, which is triggered by the accumulation of photogenerated trapped holes near the metal/organic interface. The combination of an ultrathin NTCDA film with another photoconductive pigment film in a layered structure allowed us to fabricate a photocurrent multiplication device with the desired spectral response. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117201

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Local vibrational modes (LVMs) are reported for Mg‐doped GaN grown by metalorganic chemical vapor deposition. Hetero‐epitaxial layers of GaN:Mg, either as‐grown, thermally activated, or deuterated, were investigated with low‐temperature, Fourier‐transform infrared absorption spectroscopy. The as‐grown material, which was semi‐insulating, exhibits a LVM at 3125 cm−1. Thermal annealing increases thep‐type conductivity, as established with Hall effect measurements, and proportionally reduces the intensity of this LVM. Deuteration of the activated material creates a LVM at 2321 cm−1. The isotopic shift establishes the presence of hydrogen in the vibrating complex. The new LVMs are assigned to the stretch modes of the Mg–H and Mg–D complexes in GaN, with the vibrational frequencies indicative of a strong N–H bond as recently proposed from total‐energy calculations. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117202

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The influence of polarity on the SiC crystal growth has been demonstrated using a dual‐seed technique to grow on both the C‐ and Si‐face seed simultaneously. For the investigated range of growth conditions, 4H‐SiC crystals were grown on the C‐face of 6H‐SiC seed crystals with on‐axis orientation, when the growth rate exceeded 1.2 g/h. We were never able to grow 4H‐SiC on the Si‐ face of 6H‐ or 4H‐SiC seed crystals under these growth conditions. The incorporation of nitrogen is shown to be 2–3 times higher in crystals grown on the C‐face than on the Si‐face, and is independent of both polytype and 8° off‐axis orientation. The addition of more than 15% silicon powder to the SiC sublimation source resulted in polycrystalline growth. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117203

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An optoelectronic effect based on Faraday or Kerr rotation and the quantum‐confined Stark shift is demonstrated. It is novel in that the degree of rotation is controlled by anelectricfield as opposed to amagneticfield. By applying an electric field to a quantum well structure, the Faraday rotation can be tuned into resonance, thereby varying the rotation angle of plane polarized light. We have observed a resonant rotation of 10° in GaAs at a magnetic field of 1 T. By applying a gate voltage of 2 V to a GaAs/AlGaAs superlattice structure, we observed a change in rotation of 1.3° at 2 K. The Faraday–Stark effect could be useful in electrically controlled light switches and high‐speed optical modulators. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117204

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It is well known that the gain‐bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This letter presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite ‘‘size effect’’ for multiplication regions less than approximately 0.5 &mgr;m. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117205

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The thermal activation of acceptors in wide‐gap semiconductors can be very low due to large acceptor activation energies. It is shown that superlattice doping, i.e., the composition modulation of a uniformly doped ternary semiconductor, can enhance the acceptor activation by more than one order of magnitude. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117206

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The conduction‐band offset &Dgr;Ecof Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2lattice matched to a GaAs substrate was measured by capacitance‐voltage analysis. To examine the transitivity of the band offset in the AlGaAs/InGaP/InGaAsP system, the band offsets of Al0.3Ga0.7As/In0.5Ga0.5P and In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2were investigated. The value of &Dgr;Ecfor the Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2heterostructure, estimated by adding the measured &Dgr;Ecvalues in Al0.3Ga0.7As/In0.5Ga0.5P and in In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2, agrees well with the value measured directly. We thus conclude that the transitivity rule holds well for the band offsets of an AlGaAs/InGaP/InGaAsP system lattice matched to a GaAs substrate. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117207

出版商:AIP    

年代:1996

数据来源: AIP