| Abstract [eng] |
Photoreflectance and Photoluminescence Study of Epitaxial InAs Quantum Ring Heterostructures Self-assembled InAs quantum dots (QD), embedded in InAs/GaAs/AlAs quantum well (QW), are used as active region for novel QD infrared photodetectors (QDIPs). This dots-in-a-well (DWELL) design is based on optical transitions between bound states of quantum dot and quantum well. Such photodetector scheme allows a control of peak wavelength by changing width and composition of the QW and/or by adding an external electric field. However, better knowledge about electronic states and optical properties are essential for optimising the operation of these devices. Spectroscopic photoreflectance (PR) and photoluminescence (PL) results of InAs QDs with and without strain-relieving InGaAs layer shifts the InAs QD ground-state interband transition to lower energy by ~200 meV. Comparison of experimental and calculation results revealed that the red-shift of the ground-state is attributed to increase of dot size due to reduced In content in the InGaAs-capping layer during growth. The decomposition of the InGaAs layer was also confirmed by Varsni analysis. Four QD excited-states established in modulated photoreflectance spectra and narrow photoluminescence linewidth of InGaAs-capped sample indicate a high uniformity of QDs ensemble. Comulative analysis of photoreflectance, phototransmittance, contactless electroreflectance and phototransmittance in reflection geometry revealed the influence of back-surface reflections on the PR line shape. In order to eliminate the component of photoabsorption in PR spectra DWELL sample was sanded. There is a blue-shift of all main features as the temperature is reduced in PR spectra (3-300 K). Also, it was found that temperature-dependent lineshape in PR spectra varies with photomodulaition mechanism. More detailed analysis of PR spectra disclosed that at high temperatures the line shape is influenced by the quantum-confined Stark effect. Whereas at low temperatures the line shape of PR indicated a presence of state-filling mechanisms. The Arrhenius fitting explained the PL intensity quenching in InAs QDs. In the intermediate temperatures (120-210 K) PL intensity decay is caused by the reduced carrier flow into quantum dots due to the thermal escape of electron-hole pairs from InAs wetting layer or InGaAs cap layer to GaAs/AlAs wide quantum well. However, in high temperature region (210-300 K) PL intensity quenching is related to the excitons escaping from the QD bound-state to InAs wetting layer or to InGaAs quantum well. |
