Studies on the Optical Characteristics of Heavily Si-doped InAs and Ordered InGaP
Date Issued
2011
Date
2011
Author(s)
Hong-Liao, Chi-Jing
Abstract
This thesis presents the optical characteristics of heavily Si-doped InAs, grown by gas-source molecular beam epitaxy, and InGaP, grown by metal-organic vapor phase epitaxy. In the first portion of this thesis, we report the Raman scattering of the heavily Si-doped InAs. The Raman spectra show coupled plasmon LO-phonon (PLP) mode and unscreened LO mode. The frequency of the PLP mode is slightly lower than that of the LO mode and gradually reduces to frequency of the TO mode when the carrier density increases, in conflict with the PLP mode equation. This abnormal behavior becomes less significant when we replaced the 514-nm laser by 632-nm laser. By comparing the LO wave-vector and the Thomas-Fermi screening wave-vector of each InAs bulk layer, we found that the screening effect is responsible for this abnormal behavior. The unscreened LO mode is attributed to the surface accumulation layer, whose thickness is too short to screen the LO mode. We also observed the forbidden unscreened LO mode for the samples with a carrier density higher than 5x10^19/cm^3, which is ascribed to the resonant enhanced scattering induced by space charge field of the surface layer. FTIR was used to measure the reflectance of the samples to obtain the plasma frequency. The result is in good agreement with the plasmon frequency determined from the Raman scattering.
In the second portion of this thesis, ordered InGaP material has been studied by Raman scattering and photoluminescence (PL) measurement. We used the energy gap determined from room temperature PL and the lattice mismatch determined from XRD to calculate the degree of order for each InGaP samples. Valley depth (b/a) ratio, determined from the unresolved GaP-like and InP-like LO modes, decreases with the increasing ordering degree and is close to the values reported in literature. Along [1-10] polarization, we observed two additional peaks at 354 cm-1 and 380 cm-1, which has been reported in literature and are relevant to the A(Z) mode of C3v symmetry resulting from the ordering arrangement on (1-11) or (-111) plane. The most striking is that the 380 cm-1 additional peak also appears when the measurement was taken along [110] polarization, indicating that the samples could contain ordering arrangement on (111) or (-1-11) plane.
Subjects
Raman scattering
Photoluminescence
Si-doped InAs
InGaP
Ordering effect
Screening effect
Thomas-Fermi wave-vector
Type
thesis
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