Determination of free-carrier and phonon-assisted absorptions for Si-doped GaSb thin layers (original) (raw)
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Photothermal investigations of doping effects on opto-thermal properties of bulk GaSb
Journal of Alloys and Compounds, 2009
GaSb is a direct gap semiconductor (0.72 ev) having good carriers motility and significant electro-optical potential in the near IR range. As substrate or active layer, GaSb can be employed in conjunction with many semiconductors such as (AlGa)Sb or In(AsSb) and has interesting hetero junction potential for detectors, lasers and quantum well structures. The aim of this work is to investigate the influence of doping on the opto-thermal properties (optical absorption, refractive index and thermal diffusivity) of doped and undoped GaSb bulk throw, the phothermal deflection and spectroscopic reflectivity. It is found that absorption below the gap and thermal diffusivity increases with doping concentration.
Energy & Environmental Science, 2012
GaSb-based heterostructures are tested as candidates for a hot carrier solar cell absorber. Their thermalisation properties are investigated using continuous wave photoluminescence. Non-equilibrium carrier populations are detected at high excitation levels. An empirical expression of the power lost by thermalisation is deduced from the incident power dependent carrier temperature. The experimentally determined thermalisation rate is then used to simulate the potential efficiency of a hot carrier solar cell, showing a significant efficiency improvement compared to a fully thermalised single p-n junction of similar bandgap. † This article was submitted as part of a collection highlighting research from the Advanced inorganic materials and concepts for photovoltaics symposium, at the 2011 E-MRS Bilateral Energy Conference
Fundamental characterization studies of GaSb solar cells
1991
Measured forward and reverse current versus voltage curves for GaSb cells at various temperatures and for different substrate dopant densities are modeled. The authors show that tunneling across a lower bandgap for reverse-biased GaSb cells allows nondestructive reverse current flow at low voltages. Thus, the GaSb IR cell doubles as a bypass diode, providing shading protection for the GaAs cell. Measured GaSb quantum yield curves are also modeled, and the resultant minority carrier diffusion lengths are compared with electron beam induced current measurements. It is found that the GaSb cell properties are consistent with predictions based on a direct gap single-crystal material
FUNDAI'IENTAI CHARACTERIZATION STUDTES OF GaSb SOLAR CELLS
Gallium Antimonide infrared sensitive solar cells have been used behind transparent Gallium Arsenide solar cells to fabricate mechanically stacked tandem gallium cells with energy conversion efficiencies over 30%. The GaSb cells are made using simple zinc diffusions into tellurium doped single crystal GaSb wafers. Herein, our measured forward and reverse current vs voltage curves for GaSb cells at various temperatures and for different substrate dopant densities are modeled. We show that tunneling across a lower band gap for reverse biased GaSb cells allows non destructive reverse current flow at low voltages. Thus, the GaSb IR cell doubles as a bypass diode, providing shading protection for the GaAs cell. Measured GaSb quantum yield curves are also modeled and the resultant minority carrier diffusion lengths are compared with electron beam induced current measurements. We find that the GaSb cell properties are consistent with predictions based on a direct gap single crystal material.
Bandedge absorption of GaAsN films measured by the photothermal deflection spectroscopy
Journal of Crystal Growth, 2009
The optical absorption of GaAsN films grown by molecular beam epitaxy on GaAs substrates is measured using the mirage effect photothermal deflection spectroscopy (PDS). The PDS spectra were fitted with a modified Fernelius model, which takes into account multiple reflections within the GaAsN layer and GaAs substrate. This allowed the extraction of bandedge parameters for a series of GaAsN films with N content varying from 0.24% to 1.4% N. All films show a clear Urbach absorption edge with a composition-dependent bandgap consistent with literature and Urbach slope parameters roughly 3 times larger than GaAs values.
Free-carrier absorption in Be- and C-doped GaAs epilayers and far infrared detector applications
Journal of Applied Physics, 2001
Far infrared ͑FIR͒ absorption, reflection, and transmission in heavily doped p-GaAs multilayer structures have been measured for wavelengths 20-200 m and compared with the calculated results. Both Be ͑in the range 3ϫ10 18 -2.6ϫ10 19 cm Ϫ3 ͒ and C (1.8ϫ10 18 -4.7ϫ10 19 cm Ϫ3 )-doped structures were studied. It is found that the observed absorption, reflection, and transmission are explained correctly by the model with a dominant role of free-carrier absorption in highly doped regions. High reflection from heavily doped thick layers is attractive for the resonant cavity enhanced FIR detectors.
Photothermal deflection investigation of bulk Si and GaSb transport properties
The photo-thermal deflection technique (PTD) is used to study the transport properties such as non-radiative lifetime of minority carriers (τnr), electronic diffusivity (D) and surface recombination velocity (S) in bulk silicon (Si) and gallium antimonide (GaSb) semiconductors. A generalized one-dimensional theoretical model has been also developed, and the coincidence between experimental curves giving the normalized amplitude and phase variations versus square root modulation frequency and the corresponding theoretical curves makes possible to deduce the electronic parameters cited above.
American Journal of Condensed Matter Physics, 2012
Photothermal deflection PTD is used in order to reveal the influence of Te doping on non radiative carrier lifetime for GaSb bulk sample when illuminated by a modulated and monochromatic light beam. Theoretical simulations are obtained from an adapted theoretical model, based on the resolution of both heat and carrier diffusion equations. Auger recombination coefficient obtained from the linear relation between lifetime and the inverse of squared concentration is in agreement with literature. Moreover, it is found that low n-doping reduces the surface recombination velocity S because of dangling bonds neutralisation at the surface. However for higher doping concentration, S is enhanced by Te doping.
The European Physical Journal B, 2006
Reflectance measurements from p-type GaSb:Zn epitaxial films with different hole concentrations (10 17 -10 18 cm −3 ) have been investigated over the frequency region of 100-1000 cm −1 . A minimum broadening feature corresponding to the hole plasmon was observed in the reflectance spectra. The experimental infrared spectra were well fitted using a Lorentz-Drude dispersion model. The real part ε1 of the dielectric function decreases with increasing hole concentration. However, the imaginary part ε2 increases with hole concentration in the far-infrared region. This indicates that the acoustic-and optic-phonons mainly participate in the free carrier absorption processes. The hole mobility obtained from Hall-effect measurements is slightly larger than that derived from optical measurements and the average ratio of mobilities is estimated to be 1.33. Owing to overdamping effects, the upper branch of longitudinal-optical phonon plasmon (LPP) coupled modes was observed. The upper LPP + frequency increases with hole concentration and it shows a transition from phonon-like to plasmon-like behavior. A theoretical analysis with solutions in the complex frequency plane describes these experimental results.