122 research outputs found
Minority Hole Mobility in n+ GaAs
The minority hole diffusivity, or equivalently the hole mobility, was measured in n+GaAs with the zeroâfield timeâofâflight technique. The minority hole mobility was measured for the donor doping range of 1.3Ă1017 cmâ3 to 1.8Ă1018 cmâ3 and was found to vary from 235 to 295 cm2/Vâs. At the lower doping level, the minority hole mobility is comparable to the corresponding majority hole mobility, but at 1.8Ă1018 cmâ3 the minority hole mobility was 30% higher than the majority carrier hole mobility. These results have important implications for the design of devices such as solar cells and pnpâheterojunction bipolar transistors
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Recombination Lifetimes Using the RCPCD Technique: Comparison with Other Methods
The theory and operation of the resonance-coupled photoconductive decay (RCPCD) technique is described. Examples are presented of data measured on a wide variety of sample types. The RCPCD technique has been applied to a variety of wafer and thin-film materials. Using this technique, we can measure recombination lifetime over at least three decades of injection level. We can also measure relative values of minority-carrier mobility and diffusion length. By scanning the excitation wavelength, we can measure spectral response and photoconductive excitation spectra. Deep-level impurities have been detected by several variations of RCPCD
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Modeling Minority-Carrier Lifetime Techniques that Use Transient Excess-Carrier Decay (Poster)
Microsecond Lifetimes and Low Interface Recombination Velocities in Moderately Doped n-GaAs Thin Films
We have observed lifetimes greater than 1 ps in moderately doped, thin film, n-GaAs/A1a,Gae,As double heterostructure membranes formed by etching away the substrate. We attribute these ultralong lifetimes to enhanced photon recycling caused by the removal of the substrate. Nonradiative recombination in the bulk and at the interfaces is very low; the upper limit of the interface recombination velocity is 25 cm/S.-Such long lifetimes in GaAs doped at N,= 1.3 X 10â cme3 suggest that thin-film solar cells offer a potential option for achieving very high efficiencies
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Modeling Minority-Carrier Lifetime Techniques That Use Transient Excess-Carrier Decay: Preprint
Lifetime spectroscopy is a valuable tool for the characterization of PV materials. This paper combines modeling and experimental results to illustrate the injection-level dependent response of three transient excess-carrier decay techniques
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Investigation of Deep Impurity Levels in CdTe/CdS Solar Cells
We have studied deep impurity levels of CdTe/CdS solar cells by capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and time-resolved photoluminescence (TRPL)
Zero-Field Time-of-Flight Measurements of Electron Diffusion in P+-GaAs
Minority electron diffusivities in p+-GaAs-doped NA =~1.4Ă1018 and ~1019 cm-3 have been measured in zero-field conditions with an extension of the zero-field time-of-flight technique. Extension of the technique to make it applicable to heavily doped p+-GaAs is described and zero-field data are discussed. Unexpectedly, majority carrier drag effects are not evident in a comparison of this data with recently reported high-field data. Low zero-field mobility of electrons in p+-GaAs has important implications for high-speed devices such as heterojunction bipolar transistors
A study of minority carrier lifetime versus doping concentration in nâtype GaAs grown by metalorganic chemical vapor deposition
Timeâresolved photoluminescence decay measurements are used to explore minority carrier recombination in nâtype GaAs grown by metalorganic chemical vapor deposition, and doped with selenium to produce electron concentrations from 1.3Ă1017 cmâ3 to 3.8Ă1018 cmâ3. For electron densities n0\u3c1018 cmâ3, the lifetime is found to be controlled by radiative recombination and photon recycling with no evidence of ShockleyâReadâHall recombination. For higher electron densities, samples show evidence of ShockleyâReadâHall recombination as reflected in the intensity dependence of the photoluminescence decay. Still, we find that radiative recombination and photon recycling are important for all electron concentrations studied, and no evidence for Auger recombination was observed
Comparative study of minority electron properties in p+-GaAs doped with beryllium and carbon
Minority electron properties in p+âGaAs doped with beryllium (Be) and with carbon (C) are reported. Measurements of essentially identical responses for structures differing only in dopant element demonstrate that the diffusivity (Dn) and the diffusion lengths (Ln) are the same in p+âGaAs doped to âŒ1019 cmâ3 with Beâ and Câdopants. Zeroâfield timeâofâflight analysis yields Dn=35 cm2/s and internal quantum efficiency analysis yields Ln=2.4 ÎŒm, which implies a lifetime that is approximately at the estimated radiative limit. In addition, the majority Hall mobility was also found to be identical for the Beâ and Câdoped material
The Spectral Energy Distribution of HH30 IRS: Constraining The Circumstellar Dust Size Distribution
We present spectral energy distribution (SED) models for the edge-on
classical T Tauri star HH30 IRS that indicate dust grains have grown to larger
than 50 microns within its circumstellar disk. The disk geometry and
inclination are known from previous modeling of multiwavelength Hubble Space
Telescope images and we use the SED to constrain the dust size distribution.
Model spectra are shown for different circumstellar dust models: a standard ISM
mixture and larger grain models. As compared to ISM grains, the larger dust
grain models have a shallower wavelength dependent opacity. Models with the
larger dust grains provide a good match to the currently available data, but
mid and far-IR observations are required to more tightly constrain the dust
size distribution. The accretion luminosity in our models is L_acc<0.2 L_star
corresponding to an accretion rate of 4E-9M_sun/yr. Dust size distributions
that are simple power-law extensions (i.e., no exponential cutoff) yield
acceptable fits to the optical/near-IR but too much emission at mm wavelengths
and require larger disk masses. Such a simple size distribution would not be
expected in an environment such as the disk of HH30 IRS, particularly over such
a large range in grain sizes. However, its ability to adequately characterize
the grain populations may be determined from more complete observational
sampling of the SED in the mid to far-IR.Comment: ApJ Accepte
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