Photoreflectance spectroscopy of AlGaAs/GaAs heterostructures with a two-dimensional electron gas system (original) (raw)
Related papers
Study of internal electric fields in AlGaAs/GaAs two-dimensional electron gas heterostructures
Microelectronics Journal, 2003
Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy. The spectra at room temperature show Franz -Keldysh oscillations associated to the substrate -buffer layer interface. The built-in electric field magnitude calculated from these oscillations is related with the two-dimensional electron gas (2DEG) mobility. In addition we observed two signals associated to the GaAs capping layer and to the 2DEG, respectively. q
Photoluminescence from the two-dimensional electron gas at GaAs/AlGaAs single heterojunctions
Applied Physics Letters, 1988
Liquid-helium temperature photoluminescence from GaAs/Al(0.3)Ga(0.7)As modulation-doped single heterojunctions has been studied, using excitation sources from infrared to ultraviolet. The spectra have a strong interface component, accompanied by bulk GaAs and AlGaAs band-gap luminescence. Using ultraviolet instead of infrared as the excitation, the interface signal is greatly enhanced relative to the bulk GaAs luminescence. The interface signal can be shifted to the higher energies when a semitransparent front gate is positively biased. The observations indicate that the interface luminescence comes from the recombination of the two-dimensional electrons with holes trapped at or near the interface. The peaks and the shoulders in the interface spectra appear to correspond to subbands of the two-dimensional electron gas at the interface. The results demonstrate the feasibility of doing spectroscopic studies on high-mobility electrons at single heterojunctions.
Molecular beam epitaxy growth of AlGaAs on the (631)-oriented GaAs substrates
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2008
The authors report the molecular beam epitaxy growth and characterization of AlGaAs/ GaAs͑631͒ heterostructures grown at different As 4 molecular beam equivalent pressures. The reflection high-energy electron diffraction patterns taken along the ͓−1 2 0͔ azimuth showed that the twofold reconstruction commonly observed during the GaAs-buffer layer growth is preserved during the AlGaAs deposition. The 10 K photoluminiscence ͑PL͒ characterization of the samples showed transitions related to the AlGaAs band edge, the incorporation of impurities, and deep centers. The temperature dependence of the band to band PL transition was fitted with the models developed by Varshni, Pässler, and Viña. The intensity of the PL spectra drastically decreases as the As 4 pressure is increased. Photoreflectance ͑PR͒ spectroscopy also showed the best crystal quality for the sample grown at low As pressure. The authors obtained the built-in internal electric field strength and the band-gap energy from an analysis of the PR spectra close to the GaAs band edge employing the Franz-Keldysh model.
Semiconductor Science and Technology, 2013
The photoluminescence of an electron inversion layer with a monolayer of carbon acceptors in GaAs was investigated at liquid helium temperatures. In the limit of high laser illumination the luminescence line approaches a hat shape, the expected form if the recombination center is a single isolated acceptor. At medium illumination the line takes on a trapezoidal form, and in the small illumination limit a triangular shape emerges. The line shape variations could be traced back to the interaction of the carbon acceptors which is ruled by the illumination strength. Acceptor-acceptor interactions spread the distribution of transition energies and initiate a transfer of oscillator strength. The triangular line shape at low illumination is a clear signature of an impurity band formed in the carbon monolayer.
Electron confinement in planar-doped heterostructures AlxGa1−xAs:δSi/GaAs
Materials Science and Engineering: B, 2002
Photoluminescence (PL) of the modulated doped heterostructures Al 0.33 Ga 0.67 As:dSi/Al x Ga 1(x As:dSi/Al 0.33 Ga 0.67 As/GaAs is investigated for different compositions of x . A two-dimensional electron gas (2DEG) is formed at the heterointerface Al 0.33 Ga 0.67 As/GaAs due to the electron affinity difference between the two materials. The d-doping is used to enhance the performance of quantum electronic and photoionic devices. Among these aspects, the presence of the DX centres in Al 0.33 Ga 0.67 As barrier can control the electron population in GaAs channel sub-bands. Low-temperature PL measurements show that the DX centre effects are reduced when the d-doping plane is placed in a thin Al 0.24 Ga 0.76 As quantum well (QW) embedded in the Al 0.33 Ga 0.67 As barrier, and exhibit a PL band F associated to the radiative transitions of the 2DEG. The high-energy side of the band F is extended and reflects the form of â shape of the channel conduction band. Combination of PL measurements of the band F with the results of a self-consistent Poisson Á/Schrö dinger model has demonstrated that the Fermi energy is located at 110 meV above the G conduction band minimum of the channel. The PL study of these structures also reveals the presence of a large antistokes PL (ASPL) band at low temperature, situated at 100 meV above the bandgap of Al 0.33 Ga 0.67 As. The nonlinear ASPL intensity dependence on power excitation suggests a process of two-step two-photon absorption as origin of this PL. #
Photoreflectance and Raman Study of Surface Electric States on AlGaAs/GaAs Heterostructures
Journal of Spectroscopy, 2016
Photoreflectance (PR) and Raman are two very useful spectroscopy techniques that usually are used to know the surface electronic states in GaAs-based semiconductor devices. However, although they are exceptional tools there are few reports where both techniques were used in these kinds of devices. In this work, the surface electronic states on AlGaAs/GaAs heterostructures were studied in order to identify the effect of factors like laser penetration depth, cap layer thickness, and surface passivation over PR and Raman spectra. PR measurements were performed alternately with two lasers (532 nm and 375 nm wavelength) as the modulation sources in order to identify internal and surface features. The surface electric field calculated by PR analysis decreased whereas the GaAs cap layer thickness increased, in good agreement with a similar behavior observed in Raman measurements (IL-/ILOratio). When the heterostructures were treated by Si-flux, these techniques showed contrary behaviors. P...
Study of AlxGa1−xAs/GaAs heterostructures by M-M EPES method
Materials Science and Engineering: C, 2002
Low aluminum composition x, in a series of Al x Ga 1 À x As samples, has been investigated by the multi-mode elastic peak electron spectroscopy (M-M EPES). This spectroscopy is a non-destructive method, and is very sensitive to the surface sample. Indeed, all electrons are elastically reflected from the first overlayers of the substrate (J. Surf. Anal. 5 (1) (1999) 90). Measurements of the percentage of the reflected current are depending on different parameters such as the atomic number of the substrate, the primary electron beam energy (Surf. Interface Anal. 30 (2000) 341). The EPES results must be associated to a Monte Carlo program for efficient sample interpretation. The goal of this paper is to report that the Monte Carlo model, based on a realistic description of the GaAs and AlAs materials and their surface regions allowed us to explain the EPES measurements in ternary Al x Ga 1 À x As alloys when the aluminum composition is changed.
Journal of Physics D: Applied Physics, 1998
This paper describes a nondestructive method to determine the sheet carrier density of pseudomorphic high electron mobility transistor structures by fitting the room-temperature photoluminescence (PL) spectra. The sheet carrier densities determined were in sufficiently good agreement with values determined by Hall measurements for different samples with different mole fractions, δ-doping densities and well widths. For single-doped AlGaAs/InGaAs quantum wells, the dominant emission is the transitions from the first electron subband to the first heavy hole subband, from the first electron subband to the second heavy hole subband, and from the second electron subband to the first heavy hole subband.