Photoreflectance and contactless electroreflectance spectroscopy of GaAs-based structures: The below band gap oscillation features

Journal of Applied Physics

Yuen

Bank

et al. 2007

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A fruitful approach to study the Fermi level position in GaInNAs/GaAs quantum wells (QWs) has been proposed in this paper. This approach utilizes contactless electroreflectance (CER) spectroscopy and a very simple design of semiconductor structures. The idea of this design is to insert a GaInNAs quantum well (QW) into a region of undoped GaAs layer grown on n-type GaAs substrate. The possible pinning of the Fermi level in the GaInNAs QW region modifies band bending in this system. In CER spectra both QW transitions and GaAs-related Franz-Keldysh oscillations (FKOs) are clearly observed. The analysis of QW transitions allows one to determine the band gap discontinuity at GaInNAs/GaAs interface whereas the analysis of FKOs allows one to determine the built-in electric field in the GaAs cap layer, and, finally, one is able to find the Fermi level pinning in GaInNAs QW region.

Section: Resultsmentioning

confidence: 99%

Contactless electroreflectance approach to study the Fermi level position in GaInNAs/GaAs quantum wells

Journal of Applied Physics

Yuen

Bank

et al. 2007

Self Cite

“…However, it is well known that the mechanism of electro−modulation is different for the two techniques. Thus, significant differences between CER and PR spectra can appear for some samples [60][61][62].…”

Section: Contactless Electroreflectance Vs Photo--reflectancementioning

confidence: 99%

“…an oscillation feature (OF) appear in PR spectra below the energy gap of GaAs if they are grown on n−type GaAs substrates [53,60,68,69]. Sometimes a weak OF is also observed for structures grown on semin− sulating GaAs substrates [61]. In general such an OF is an unwanted signal which complicates the analysis of optical transitions in QWs and/or QDs.…”

Section: Contactless Electroreflectance Vs Photo--reflectancementioning

confidence: 99%

“…This finding shows that the OF's origin is the modulation of the refractive index in the sample due to the generation of additional carriers by the pump beam (i.e., the laser beam). In the case of CER spec− troscopy, any additional carriers are not generated during the modulation hence CER spectra are free of OFs [60,61]. few examples of CER and PR spectra measured for different structures grown on GaAs substrate (n−type and semi−isola− ting (SI) type) are presented below.…”

Section: Contactless Electroreflectance Vs Photo--reflectancementioning

confidence: 99%

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Contactless electroreflectance spectroscopy of optical transitions in low dimensional semiconductor structures

Misiewicz

Opto-Electronics Review

2012

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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.

“…However, their influence has been observed previously in a form of the socalled below band gap oscillations, i.e., an interference effect related to the modulation of the refractive index difference between two parts of the structure ͑e.g., doped substrate and undoped buffer͒. 13,14 In the case of a quantum dot structure the properties of these nanometer scale objects can be much easier modified due to loading them with charge carriers. In general, the possible modulating factors which may contribute to the QD photoreflectance signal can be divided into two groups: ͑i͒ photoinduced electromodulation of the built-in electric fields and hence modulating the QD optical transitions due to quantum confined Stark effect ͑this factor is assumed to be the dominating one for most of quantum well structures͒; ͑ii͒ modulation of the dot properties due to the appearance of carriers in the QD layer, e.g., self-consistent modification of the confinement potential, many-body effects important at higher carrier concentrations, changes in the dot material refractive index, effect of filling the dot states of a whole inhomogeneous QD ensemble according to the Boltzman distribution, etc.…”

Section: Introductionmentioning

confidence: 99%

On the modulation mechanisms in photoreflectance of an ensemble of self-assembled InAs∕GaAs quantum dots

Motyka

Sęk

Journal of Applied Physics

et al. 2006

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We present the investigation of the modulation mechanisms in photoreflectance (PR) spectroscopy of an ensemble of self-assembled semiconductor quantum dots (QDs). In order to distinguish between possible factors contributing to the total modulation efficiency of QD transitions, a photoreflectance excitation experiment has been performed on an InAs∕GaAs quantum dot structure grown by solid-source molecular beam epitaxy. It has been observed that the intensity of PR features related to QDs changes in a function of the wavelength of the pumping laser, tuned from above-GaAs band gap down to below wetting layer ground state transition. Based on this dependence we have shown that most of the QD PR signal intensity originates from the modulation of the built-in electric field caused by carriers photogenerated in GaAs layers. We also conclude that the modulation of QD transitions related to a possible modification of the dot properties due to filling them with carriers is negligible in PR experiment on an ensemble of dots. An additional confirmation of the PR results has been obtained by using contactless electroreflectance (CER), demonstrating that the line shape of PR and CER QD resonances is almost identical in both spectra. Thus, the QD transitions can be analyzed by using the standard low field line shape functional form applicable in any electromodulation spectroscopy.