Article:Cechavicius, B., Kavaliauskas, J., Krivaite, G. et We present an optical study of beryllium ␦-doped GaAs/ AlAs multiple quantum well ͑QW͒ structures designed for sensing terahertz ͑THz͒ radiation. Photoreflectance ͑PR͒, surface photovoltage ͑SPV͒, and wavelength-modulated differential surface photovoltage ͑DSPV͒ spectra were measured in the structures with QW widths ranging from 3 to 20 nm and doping densities from 2 ϫ 10 10 to 5 ϫ 10 12 cm −2 at room temperature. The PR spectra displayed Franz-Keldysh oscillations which enabled an estimation of the electric-field strength of ϳ20 kV/ cm at the sample surface. By analyzing the SPV spectra we have determined that a buried interface rather than the sample surface mainly governs the SPV effect. The DSPV spectra revealed sharp features associated with excitonic interband transitions which energies were found to be in a good agreement with those calculated including the nonparabolicity of the energy bands. The dependence of the exciton linewidth broadening on the well width and the quantum index has shown that an average half monolayer well width fluctuations is mostly predominant broadening mechanism for QWs thinner than 10 nm. The line broadening in lightly doped QWs, thicker than 10 nm, was found to arise from thermal broadening with the contribution from Stark broadening due to random electric fields of the ionized impurities in the structures. We finally consider the possible influence of strong internal electric fields, QW imperfections, and doping level on the operation of THz sensors fabricated using the studied structures.

Radiative recombination spectra of p -type δ -doped Ga As ∕ Al As multiple quantum wells near the Mott transition Photoreflectance and surface photovoltage spectroscopy of beryllium-doped Ga As ∕ Al As multiple quantum wells J. Appl. Phys. 98, 023508 (2005); 10.1063/1.1978970Effect of quantum-well confinement on acceptor state lifetime in δ -doped GaAs/AlAs multiple quantum wells Beryllium and silicon ␦-doped GaAs/ AlAs multiple quantum wells ͑MQWs͒ were designed and fabricated for selective sensing of terahertz radiation. Optical characterization of the structures by photoreflectance spectroscopy has indicated a presence of built-in electric fields-from 18 up to 49 kV/ cm depending on the structure design-located mainly in the cap and buffer layers, but do not penetrating into the MQWs region. Terahertz sensing under normal incidence via impurity bound-to-unbound transitions is demonstrated in photocurrent experiments within 0.6-4.2 THz in silicon-doped MQWs and 3.5-7.3 THz range in beryllium-doped MQWs at low temperatures.

Articles you may be interested inEffect of carriers transfer behavior on the optical properties of InAs quantum dots embedded in AlGaAs/GaAs heterojunction J. Appl. Phys. 107, 074307 (2010); 10.1063/1.3371356Optical transitions and band gap discontinuities of GaInAsSb/AlGaAsSb quantum wells emitting in the 3 μ m range determined by modulation spectroscopy Contactless electroreflectance of In As ∕ In 0.53 Ga 0.23 Al 0.24 As quantum dashes grown on InP substrate: Analysis of the wetting layer transition On the modulation mechanisms in photoreflectance of an ensemble of self-assembled In As ∕ Ga As quantum dots Optical transitions in vertically stacked InAs quantum dot ͑QD͒ superlattice ͑SL͒ with and without AlAs barriers were examined by photo-and electroreflectance techniques. The interband transitions corresponding to the QD, wetting layer ͑WL͒, and InAs/GaAs/AlAs SL have been identified. Experimental data and numerical calculations show that blueshifts and enhancement in the intensity of WL-related optical transitions in an InAs/GaAs/AlAs SL originate mainly due to off-center position of the QD layers in the quantum wells. The appearance of multiple WL-related features in the modulated reflectance spectra was revealed and discussed.

We present a photoreflectance (PR) study of multi-layer InAs quantum dot (QD) photodetector structures, incorporating InGaAs overgrown layers and positioned asymmetrically within GaAs/AlAs quantum wells (QWs). The influence of the back-surface reflections on the QD PR spectra is explained and a temperature-dependent photomodulation mechanism is discussed. The optical interband transitions originating from the QD/QW ground-and excited-states are revealed and their temperature behaviour in the range of 3-300 K is established. In particular, we estimated the activation energy ($320 meV) of exciton thermal escape from QD to QW bound-states at high temperatures. Furthermore, from the obtained Varshni parameters, a strain-driven partial decomposition of the InGaAs cap layer is determined. V C 2015 AIP Publishing LLC.

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