Modulation effects near the GaAs absorption edge

Abstract

We show that the large features often found below the band gap in modulated spectra of GaAs samples are linked not only to impurities but also to back-surface reflection effects. Their proximity to the band edge depends on the geometry of the cavity in which the multiple reflections occur, the impurity species, and the temperature. Impurity contributions to the energy-dependent absorption coefficient become manifest in a multiple-reflection-enhanced reflectance edge. Externally applied perturbations modulate this reflectance edge, thereby producing first-derivative-like spectral features. At 5 K the extrema of the impurity-related features roughly correspond to the energies associated with donor and acceptor states. However, at room temperature they disagree significantly and therefore do not specify an impurity species with certainty.

Temperature-dependent modulated reflectance of InAs/InGaAs/GaAs quantum dots-in-a-well infrared photodetectors

“…Effects of the back-surface reflections Before presenting the temperature-dependent spectroscopic data, let us consider the role of BSR on modulated reflectance spectra in more detail. Previously, the BSR effect on PR spectra has been studied for GaAs, 19,20 but not for QD structures. The probability of an absorption process occurring in the QD layer is defined by the absorption crosssection, r ¼ a/N, where a is absorption coefficient and N is the QD sheet density.…”

Below band gap photoreflectance transitions in epitaxial GaN

“…The 3.466-eV peak can be decomposed into two peaks at 3.467 eV and 3.455 eV. We attributed these peaks to a neutral donor bound exciton 12 and a neutral acceptor bound exciton, 11 respectively. The neutral donor is likely Si Ga , 16,17 since the sample was doped with Si.…”

“…However, other experiments showed that BLS resulted from back surface reflection effects. 9,10 Tober et al 11 attributed the BLS in their GaAs samples to both impurities and back surface reflections.…”

Characterization of Gap States in an Amorphous SiN[sub x] Film Grown on GaAs Substrate Using Modulation Spectroscopic Techniques

“…2 is due to the mechanism of back surface reflection effects ͑BSR͒ of the modulation spectra. 12,13 In the influence of BSR, the contribution of the imperfection to the energy-dependent absorption coefficient became manifest in a multiple-reflection-enhance reflectance edge. 13 From Fig.…”

“…12,13 In the influence of BSR, the contribution of the imperfection to the energy-dependent absorption coefficient became manifest in a multiple-reflection-enhance reflectance edge. 13 From Fig. 2, the energies of E D1 , E D2 , E D3 , E D4 , E D6 , and E D8 in the PzR spectra show the temperature-insensitive character at 15 and 300 K. These features are most probably related to the transitions of dangling bond to dangling bond or dangling bond to conduction-band bottom ͑E C ͒ of a-SiN x .…”