摘要:

The optical properties ofn-type GaN are investigated for Si doping concentrations ranging from5×1016to7×1018 cm−3.The photoluminescence linewidth of the near-band gap optical transition increases from 47 to 78 meV as the doping concentration is increased. The broadening is modeled in terms of potential fluctuations caused by the random distribution of donor impurities. Good agreement is found between experimental and theoretical results. The intensity of the near-band-gap transition increases monotonically as the doping concentration is increased indicating that nonradiative transitions dominate at a low doping density. The comparison of absorption, luminescence, reflectance, and photoreflectance measurements reveals the absence of a Stokes shift at room temperature demonstrating the intrinsic nature of the near-band edge transition. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119689

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Surfactant-mediated epitaxy (SME) allows the growth of smooth, continuous, relaxed, and principally defect free Ge films directly on Si(111); however, the very high surfactant doping level in the range of the solid solubility limit made them unacceptable for most device applications. By using high temperature SME we have reduced the Sb surfactant background doping level by more than three orders of magnitude. This is attributed to an enhanced surfactant segregation without kinetic limitations. The low Sb incorporation has been determined by an electrical characterization: An electron concentration of1.1×1016 cm−3and a very high electron Hall mobility of3100 cm2/V sat 300 K (12 300 cm2/V sat 77 K) suggest an interesting potential of SME grown Ge films for future device applications. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119690

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The characteristics of ground and excited state luminescent transitions inIn0.4Ga0.6As/GaAsandIn0.35Ga0.65As/GaAsself-organized single- and multiple-layer quantum dots forming the active regions of lasers have been studied as a function of incident excitation intensity, temperature and number of dot layers. The results have been correlated with molecular beam epitaxial growth conditions. The threshold excitation density for the saturation of the ground state increases with the number of dot layers and no saturation is observed in samples with more than six dot layers up to an excitation power density of2 kW/cm2.The luminescent decay times for the ground and excited states are around 700 and 250 ps, respectively, almost independent of the number of dot layers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119691

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The current density–voltage characteristics of poly(dialkoxyp-phenylene vinylene) based polymer are investigated as a function of temperature. Model calculations show that the differences between single and double carrier devices can be well understood by taking into account a bimolecular recombination process. It is found that the bimolecular recombination is thermally activated with an identical activation energy as measured for the charge carrier mobility. This demonstrates that the recombination process is of the Langevin type, and explains why the conversion efficiency (photon/carrier) of a polymer light-emitting diode is temperature independent. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119692

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Anisotropy of electrical and optical properties in&bgr;-Ga2O3single crystals has been investigated at room temperature. The conductivity and mobility of the degenerate sample along the direction ofbandcaxes are38 &OHgr;−1 cm−1,46 cm2 V−1 s−1,and2.2 &OHgr;−1 cm−1,2.6 cm2 V−1 s−1,respectively. The absorption edges of the insulating sample for light polarizedE//bandE//cwere 4.79 and 4.52 eV, respectively. The rate of the band gap widening with increasing carrier concentration was much larger forE//bthanE//c. The origin of these properties are discussed by considering the crystal and electronic structure of&bgr;-Ga2O3.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119693

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report time resolved studies of optically induced circular dichroism in room temperature GaAs/AlGaAs multiple quantum wells to resolve spin-dependent and spin-independent contributions to exciton saturation. Phase-space filling and Coulomb contributions were separated by spin dependence while the effects of broadening and screening were distinguished using different pulse bandwidths. Bound and free carrier contributions were compared by observing the temporal dependence of the circular dichroism on femtosecond timescales. The spin independent contribution to exciton saturation was found to be independent of whether the carriers were bound or free. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119694

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the preferred substitution of Ge in InP by altering the local stoichiometry of the InP substrate. By co-implanting P with Ge to create a group V-rich environment, we directly observed an enhancement of the Ge substituting the In sublattice. A corresponding increase in then-type conductivity by as much as three times was also observed in the Ge and P co-implanted sample. However, due to the altered local stoichiometry, the Ge solubility in InP was reduced by a factor of 2. The residual crystalline damage in the P co-implanted InP after annealing was also decreased due to the compensation of the nonstoichiometry related damage by the excess P in the middle of the implanted region. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119695

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Schottky barrier height and ideality factor of Pt onp-type strained Si (grown on a graded relaxedSi0.82Ge0.18buffer layer) have been investigated in the temperature range (90–150 K) using the current-voltage characteristics and are found to be temperature dependent. While the ideality factor decreases with an increase in temperature, the barrier height increases. Simulation based on a drift-diffusion emission model has been used to explain the experimental results. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119696

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ann-type phosphorous (P) doped epitaxial diamond film with high conductivity was grown on a C(001) substrate by gas source molecular beam epitaxy using methane and tri-n-butylphosphine. The electrical conductivity of the diamond film was measured to be 0.33(&OHgr; cm)−1at 23 °C with its activation energy to be 0.12 eV. The Hall measurements showedn-type conduction and a carrier concentration of1.6×1018cm−3at 400 °C, which is comparable to the P concentration determined by secondary-ion-mass spectroscopy. These indicate the formation of shallow P donors with high electrical activation efficiency. Ap-njunction diode was fabricated by growing a P-doped epitaxial film on a boron-doped C(001) substrate, which showed for the first time a rectification ratio of∼103at 10 V. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119922

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The direct observation of free A, B, and C excitons withn=2in hexagonal bulk gallium nitride (GaN) by two-photon spectroscopy is reported. From these data, the band gaps, exciton binding energies, and hole masses for the three uppermost valence bands are calculated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119697

出版商:AIP    

年代:1997

数据来源: AIP