Photoreflectance and Raman Study of Surface Electric States on AlGaAs/GaAs Heterostructures (original) (raw)
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Springer Proceedings in Physics, 2009
The photoreflectance (PR) is a sensitive optical method for examining the surface and interface properties of semiconductors . The important substrates that are available for light emitting technology are GaAs and InP. In this report, we simulate PR Spectra of GaAs in two cases: single-layer model (surface field is homogeneous in depth d), and multi—layer model (surface field decreases with depth d). By the multi-layer model, we received simulation results that are very similar to the experimental results. Important semiconductor materials exploited in optoelectronics are the AlxGa1–xAs alloys which are lattice matched very well to GaAs substrates. With the multi-layer model we simulated the PR spectra of the heterojunction structure AlxGa1–xAs / GaAs / GaAs (x = 0.05) for heterojunction— LEDs. The two-channel (X,Y) lock-in phase analysis is one of the most powerful methods for studying multi-component PR spectra . In this report, we set up the phase diagram in three-dimensions: X(E...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2002
We report a study of AlGaAs/GaAs semiconductor heterostructures with a two-dimensional electron gas system grown under different conditions by molecular beam epitaxy in three different laboratories. We performed photoreflectance ͑PR͒ measurements of this set of samples and analyzed the Franz-Keldysh oscillations associated with the E 0 transition of GaAs. We found that the sample with the highest electron mobility, as observed in Hall measurements at 77 K exhibited the lowest electric field strength. In addition, the 12 K photoluminescence ͑PL͒ spectra of the samples revealed intense and narrow free exciton luminescence in the sample with the highest electron mobility, while samples with lower mobility values showed impurities related PL lines. It is suggested that the electron mobility is affected by unintentional C impurities, which act like dispersion centers in the 2-DEG and increase the internal electric fields in the GaAs region. On the other hand, the PR spectra close to the AlGaAs band-gap energy region presented broad PR signals, due to the Si-doping in the alloy. The sample with the highest quality presented the most intense AlGaAs PR signal. We believe that low AlGaAs PR signal intensities are caused by unintentional incorporation of impurities during the preparation of the samples, which degrade the optical properties of the alloy.
Journal of Physics: Conference Series, 2010
Photomodulation Raman spectroscopy (PM-RS) has been employed to study the surface depletion electric field Es and to monitor the change in surface charge density in n-type GaAs, using the forbidden LO phonon scattering for low doping samples and coupled plasmon-LO phonon modes for high doping samples. In PM-RS, the photomodulating pumping beam (PB) is incident on the sample while the Raman measurements are in progress hence PM-RS can be viewed as a pump-probe technique. The photogenerated carriers partly neutralize the surface charges. Two different GaAs surfaces (011) with low and moderate doping density and (001) with high doping density were used. The total surface charge density has been obtained as a function of the PB intensity considering a constant depletion electric field for the lower doping sample of (011) surface and using the dependence of the unscreened LO phonon on the depletion width for the higher doping samples of (001) surface. The minority carrier's lifetime was also determined through dynamical measurements for the PM-RS of the low doping sample as ≈ 21 s, in a good agreement with other techniques
Hydrogen passivation of AlxGa1−xAs/GaAs studied by surface photovoltage spectroscopy
Physica B: Condensed Matter, 1999
We study the e!ect of hydrogen passivation on Al V Ga \V As grown by liquid-phase epitaxy (LPE) on semi-insulating GaAs. Using surface photovoltage (SPV) spectroscopy and Hall measurements we investigate the e!ect of hydrogenation on Al V Ga \V As epilayers with electron concentrations in the range 10}10 cm\. We measure the minority carrier di!usion length in the as-grown Al V Ga \V As epilayers to be in the range 0.1}0.8 m and to increase signi"cantly upon hydrogenation. Hydrogen passivation of interface states at the heterojunction is demonstrated for epilayers with low carrier concentration. We apply the result from the SPV measurements to speculate on the band bending at the heterojunction.
Role of surface and interface states on the performance of GaAs based photodetectors
2019
The effect of surface and interface states of various GaAs based structures such as n + GaAs, n-n + GaAs and p-in GaAs are investigated for understanding the detector performance. These structures are grown by metal organic vapor phase epitaxy (MOVPE). Surface photovoltage spectroscopy is performed in these structures to investigate the role of surface and interface states on the absorption spectra. Decrease in surface photovoltage signal with increased chopping frequency indicate the presence of slow temporal response states. These states get passivated by growing homo epitaxial layer of GaAs on n + GaAs substrate. Subsequently, for the isolation of surface and interface states on the p-in detector structure, n-n + GaAs and p-in GaAs structures are investigated separately. Further, the detectors of these structures are developed and their spectral response are recorded at room temperature. The responsivity values are evaluated by varying the incident power of 690 nm laser. Ten times increase in responsivity is observed in p-in GaAs photodetector compared to n-n + GaAs photodetector. A low dark current (~ 0.5 nA) is also obtained in p-in GaAs photodetector which qualifies its better device performance.
Photoreflectance characterisation of GaAs and GaAs/GaAIAs structures grown by MOCVD
Advanced Materials for Optics and Electronics, 1995
Epitaxial undoped and doped (Si and Zn) GaAs and GaAlAs layers as well as heterostructures of GaAs/GaAIAs have been grown in an atmospheric pressure, vertical MOCVD system. Room temperature photoreflectance (PR) has been applied to characterise the layers and heterostructures as well as multiple quantum wells. The surface-and interface-related PR has been studied by application of Kramers-Kronig analysis. A decomposition of the PR spectrum into spectra connected with the surface region and with the interface has been proposed.
Photoemission study of LT-GaAs
Journal of Alloys and Compounds, 2004
The electronic structure of GaAs (1 0 0) grown by low-temperature molecular beam epitaxy was investigated by means of photoemission spectroscopy. Slight differences are found in the valence band spectra of GaAs layers grown at different As 2 /Ga flux ratios. Analysis of As 3d core level spectra does not indicate qualitative differences in respect to high temperature grown GaAs (1 0 0) layers. The Ga 3d core level spectra include a new component in comparison to the spectra of high temperature grown GaAs. The origin of this component is attributed to high density of As antisites in low-temperature grown GaAs.
Structural characterization of AlGaAs:Si/GaAs (631) heterostructures as a function of As pressure
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2016
AlGaAs:Si/GaAs heterostructures were grown on (631) and (100) GaAs substrates and studied as a function of the As cell beam equivalent pressure. High-resolution x-ray diffraction patterns showed that the highest quality AlGaAs epitaxial layers were grown at P As ¼ 1.9 Â 10 À5 for (100)-and P As ¼ 4 Â 10 À5 mbar for (631)-oriented substrates. Raman spectroscopy revealed higher crystalline quality for films grown on (631) oriented substrates. The GaAs-and AlAs-like modes of the AlGaAs(631) films exhibited increased intensity ratios between the transverse optical phonons and longitudinal optical phonons with increasing P As , whereas the ratios were decreased for the (100) plane. This is in agreement with the selection rules for (631) and high-resolution x-ray diffraction observations. Anisotropy and surface corrugation of the AlGaAs(631) films also were characterized using atomic force microscopy and Raman spectroscopy. V