摘要:

We present results of a time-resolved photoluminescence study of the dynamics of photoexcited carriers inAlxGa1−xN/GaNdouble heterostructures (DHs). The carrier dynamics including generation, diffusion, spontaneous recombination, and nonradiative relaxation were studied by examining the time decay of photoluminescence associated with the spontaneous recombination from the samples. The temporal evolution of the luminescence from the GaN active layers of the DH samples was found to be governed by a carrier–diffusion dominated capture process. The determination of the capture time for the carriers drift and diffusion into the GaN active region, in addition to the effective lifetimes of the spontaneous recombination for carriers in the AlGaN cladding layers and the GaN active region, allows an estimation of the diffusion constants for the minority carriers in theAlxGa1−xNcladding layers of the DHs. Our results yield a diffusion constant of2.6 cm2/sforAl0.03Ga0.97Nand1.5 cm2/sforAl0.1Ga0.9Nat 10 K. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366101

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a Monte Carlo study of shot noise suppression in double barrier nonresonant heterostructure GaAs/AlGaAs diodes. Substantial suppression up to a factor 0.5 is found in agreement with a formula of de Jong and Beenakker [Phys. Rev. B51, 16 867 (1995)] obtained within Langevin–Boltzmann theory. The spectrum of current noise exhibits two resonant peaks before the cutoff region. These peaks are associated with certain features of the carrier motion due to reflections from the first barrier and oscillations inside the GaAs well, respectively. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366102

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermoelectric power (TEP) properties of graphite nanotubule bundles were measured in the range 80–280 K. It was found that the TEP is positive and the magnitude at 280 K reaches about an order of +15 &mgr;V/K, far larger than that in highly oriented pyrolytic graphite. Moreover, in the studied range, the TEP can be approximately described by the formulaS(&mgr;V)=0.167T−(70.2+0.085T)e−302.5/Tderived based on a two-band model. The experimental results support such an idea that in the buckybundles both kinds of nanotubes, i.e., metallic tubes with a highly mobile velocity and semiconductive tubes with a narrow energy gap are included. The Fermi energy of the valence band for the metallic tubes is about −0.22 eV, and the average effective energy gap of the semiconductive tubes is estimated at about 52.2 meV. This conclusion is in good agreement with the theoretical predictions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366161

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.366551

出版商:AIP    

年代:1997

数据来源: AIP