Contactless electroreflectance spectroscopy of optical transitions in low dimensional semiconductor structures

Abstract

The authors present the application of contactless electroreflectance (CER) spectroscopy to study optical transitions in low dimensional semiconductor structures including quantum wells (QWs), step-like QWs, quantum dots (QDs), quantum dashes (QDashes), QDs and QDashes embedded in a QW, and QDashes coupled with a QW. For QWs optical transitions between the ground and excited states as well as optical transitions in QW barriers and step-like barriers have been clearly observed in CER spectra. Energies of these transitions have been compared with theoretical calculations and in this way the band structure has been determined for the investigated QWs. For QD and QDash structures optical transitions in QDs and QDashes as well as optical transitions in the wetting layer have been identified. For QDs and QDashes surrounded by a QW, in addition to energies of QD and QDash transitions, energies of optical transitions in the surrounded QW have been measured and the band structure has been determined for the surrounded QW. Finally some differences, which can be observed in CER and photo-reflectance spectra, have been presented and discussed for selected QW and QD structures.

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

“…We speculate that this phenomenon is associated with the short modulation depth in CER spectroscopy. 16 …”

“…Room temperature CER experiments were carried out using a capacitor-like system. 9,14,16 To provide a modulating electrical field, a sinetype AC signal from a high voltage amplifier (Trek 609E-6) of $1.5 kV peak-to-peak amplitude and $190 Hz frequency was applied to the top transparent electrode. A phasesensitive detection technique, with a lock-in amplifier, was used in all spectroscopic measurements.…”

“…24 While using the index m ¼ 3 yields the first derivative of a Gaussian absorption profile, 27 which is acceptable for quantum systems with inhomogeneously broadened energy levels. The moduli of individual PR resonances (individual optical transitions) were evaluated from fitting the PR spectra according to 16 jDq…”

“…To date, these methods have been successfully applied to characterize a number of low-dimensional systems and nanostructures. [8][9][10][11][12][13][14][15][16][17] But despite the previous extensive studies of quantum heterostructures, the temperature-dependent modulated reflectance spectra of multi-layer DWELL photodetector structures with doped QDs have yet to be investigated extensively, and further work is still needed to clarify the underlying mechanisms.…”

Temperature-dependent modulated reflectance and photoluminescence of InAs–GaAs and InAs–InGaAs–GaAs quantum dot heterostructures

“…1.55 µm wavelength) [1] and photodetectors (3-5 µm, [8][9][10][11][12] µm) [2]. In particular, InAs-GaAs quantum dots (QDs) have been used for QD infrared photodetectors (QDIPs), exploiting intraband electronic transitions between bound-state of QD and continuum.…”