Sasikala Ganapathy

Photoluminescence study of InAs quantum dots embedded in GaNAs strain compensating layer grown by metalorganic-molecular-beam epitaxy

Self-assembled InAs quantum dots (QDs) embedded in GaN0.007As0.993 strain compensating layers have been grown by metalorganic-molecular-beam epitaxy on a GaAs (001) substrate with a high density of 1×1011 cm−2. The photoluminescence properties have been studied for two periods of InAs quantum dots layers embedded in GaN0.007As0.993 strain compensating layers. Four well-resolved excited-state peaks in the photoluminescence spectra have been observed from these highly packed InAs QDs embedded in the GaN0.007As0.993 strain compensating layers. This indicates that the InAs QDs are uniformly formed and that the excited states in QDs due to the quantum confinement effect are well defined. This is explained by tensile strain in GaNAs layers instead of the usual GaAs layers to relieve the compressive strain formed in InAs QDs to keep the total strain of the system at a minimum.

GaNAs as Strain Compensating Layer for 1.55 µm Light Emission from InAs Quantum Dots

GaNAs strain-compensating layers (SCLs) are applied to bury InAs quantum dots (QDs) grown on GaAs substrates. The main idea is the compensation of the compressive strain induced by InAs QDs with the tensile strain in the GaNAs SCLs to keep the total strain of the system minimum. The application of the GaNAs SCLs resulted in a systematic shift of photoluminescence (PL) peaks of the InAs QDs toward the longer wavelengths with the increase of the nitrogen (N) composition in GaNAs, and luminescence at a wavelength of 1.55 µm has been achieved from the InAs QDs for the N composition of 2.7% in the GaNAs SCL. This result is promising for the application of GaNAs SCL for InAs-QDs-based long-wavelength light sources for optical-fiber communication systems.

Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers

Two kinds of self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence (PL) measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs.

Observation of reflection high-energy electron diffraction oscillation during metalorganic-molecular-beam epitaxy of AlAs and control of carbon incorporation

The in situ observation of reflection high-energy electron diffraction (RHEED) oscillations during the metalorganic-molecular-beam epitaxy deposition of AlAs and AlGaAs epitaxial layers is reported. In situ RHEED oscillations as well as atomic force microscopy measurements confirmed the layer-by-layer growth of the AlAs as well as the AlGaAs layers on GaAs substrates. RHEED oscillation was successfully applied to the precise control of the AlAs/GaAs superlattices and of the alloy compositions in the AlGaAs alloys. High-resolution x-ray diffraction and Hall effect measurements revealed the unintentional doping of carbon into the AlGaAs layers, but it was found that the increase in the V/III ratio is able to reduce the carbon incorporation.

Effect of GaNAs strain compensating layer over InAs quantum dots grown by MOMBE

We demonstrated the 1.55 /spl mu/m light emission at room temperature from self-assembled InAs quantum dots embedded inside the GaNAs strain-compensating layer. InAs quantum dots have been capped with tensile strained GaNAs instead of InGaAs and GaAs to compensate the compressive strain formed due to InAs QDs to keep the total strain of the system minimum; as a result the PL peak of InAs QDs shifts towards longer wavelength depending on the N% in GaNAs. The wavelength of 1.55 /spl mu/m is the longest wavelength so far achieved in self-assembled quantum dots grown on GaAs substrates, which would be promising for application to light source in long-wavelength optical-fiber communication system.

MOMBE Growth and Characterization of III–V-N Compounds and Application to InAs Quantum Dots

This chapter deals with mainly two topics. One is the metalorganic molecular-beam epitaxy (MOMBE) of III-V-N compounds such as GaAsN, GaInNAs, and GaAsNSe. The relation of the In and N incorporations is known to depend on the growth techniques and this topic will be discussed to give some unified understanding. The other is the discussion on the more general physics-oriented special features of III-V-N compounds such as the temperature dependence of the GaAsN energy gap and the strain compensation of InAs quantum dots by combining with GaAsN.

Improved luminescence efficiency of InAs quantum dots by nitrogen-induced strain compensation with GaNAs burying layers

Luminescence efficiency of InAs quantum dots (QDs) was shown to improve with strain compensation of the compressive strain in InAs QDs with tensile-strained GaNAs burying layers. The improved luminescence efficiency is discussed with the viewpoint of the average strain compensation in the strained semiconductor system. The red shift of the luminescence peak up to 1.55 /spl mu/m is also discussed from the same viewpoint of the strain compensation. The valence-force field model calculation of the strain field in the InAs QDs buried with the GaNAs strain compensating layer shows that the strain induced by nitrogen (N) atoms is significant and localized to respective N atoms and the more detailed information how the N atoms are incorporated during the burying process of the QDs with the GaNAs layers is necessary for the full description.

InAs-quantum-dots-based light emitting diodes with GaNAs strain-compensating layers

GaNAs strain compensating layers have been used to obtain 1.5 /spl mu/m luminescence from InAs quantum dots, and this fundamental scheme was demonstrated with light emitting diodes operating at room temperature.