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Abstract

We studied the different carrier kinetic mechanisms involved into the interband absorption of quantum dots (QDs) by photocurrent spectroscopy. It was shown that in vertically coupled InGaAs QDs an effective carrier emission, collection and separation take place due to minizone formation. The possibility for the incorporation of vertically-coupled QDs into solar cells (SC) without any deterioration of structural quality of the p-i-n-junction has been shown. Due to the additional absorption of solar spectrum in QD media and the subsequent effective separation of photogenerated carriers, an increase (~1%) in short-circuit current density (Jsc) for the QD SC-devices has been demonstrated. However the insertion of QDs into intrinsic region reduced the open circuit voltage (Voc) of such devices. Moving the QD array in the base layer as well as including the Bragg reflector (BR) centered on 920 nm resulted in increase of the Voc. Moreover an improved absorption in the QD media for SC with BR led to further increase of Jsc (~1%). The efficiency for QD SCs at the level of 25% (30 suns AM1.5D) has been demonstrated.

We studied the different carrier kinetic mechanisms involved into the interband absorption of quantum dots (QDs) by photocurrent spectroscopy. It was shown that in vertically coupled InGaAs QDs an effective carrier emission, collection and separation take place due to minizone formation. The possibility for the incorporation of vertically-coupled QDs into solar cells (SC) without any deterioration of structural quality of the p-i-n-junction has been shown. Due to the additional absorption of solar spectrum in QD media and the subsequent effective separation of photogenerated carriers, an increase (~1%) in short-circuit current density (Jsc) for the QD SC-devices has been demonstrated. However the insertion of QDs into intrinsic region reduced the open circuit voltage (Voc) of such devices. Moving the QD array in the base layer as well as including the Bragg reflector (BR) centered on 920 nm resulted in increase of the Voc. Moreover an improved absorption in the QD media for SC with BR led to further increase of Jsc (~1%). The efficiency for QD SCs at the level of 25% (30 suns AM1.5D) has been demonstrated.

Low threshold current density (AlInGa)As/GaAs lasers based on InGaAs quantum dots (QDs) are grown by metal organic chemical vapour deposition (MOCVD). Quantum dots deposited at 490° C and covered with GaAs are directly revealed in the active region. On a transmission electron microscopy (TEM) image of the laser structure no large clusters or dislocations are found over a macroscopic distance. We show that the properties of QD lasers can be strongly improved if the QDs are confined by Al0.3Ga0.7As barriers and the cladding layers are grown at high temperature. Optimisation of the laser structure geometry allows extension of the range of ultrahigh temperature stability (T0=385 K) of the threshold current to 50° C.

Very strongly electronically coupled zero-dimensional structures were grown using metal-organic chemical vapour deposition (MOCVD). The method is based on formation of first a sheet with InGaAs pyramids on the GaAs (100) surface, and subsequent alternate short-period GaAs-InGaAs deposition with GaAs layer thickness much smaller than the pyramid height. This results in formation of column-like InGaAs structures. Each structure has a characteristic lateral size of ?23 nm at the top and is composed of many closely packed InGaAs parts separated by only 2-3 monolayer-thick GaAs barrier layers. Each upper InGaAs part in a column is progressively larger than the lower parts. The full width at half-maximum of luminescence of 28 meV at 8 K indicates good average uniformity of the electronically coupled dot ensemble. Effective tunability of the emission wavelength at and around 1.3 µ m can be realized using this approach.