Cross-Sectional Scanning Tunneling Microscopy Studies of In _1-xGa_x Sb/InAs Quantum Dots

Abstract:

This thesis focuses on the characterization of In _0,4 Ga _0,6 Sb/InAs and InSb/InAs quantum dots using Cross-Sectional Scanning Tunneling Microscopy (X-STM). Quantum dots (QDs) are small and spatially confined semiconductor nanostructures with a size-dependent band gap. This property makes them very attractive for devices such as sensors, solar cells and lasers. The QDs analyzed in this thesis were grown using Metal-Organic Vapor Phase Epitaxy (MOVPE) and are meant to be utilized in long wavelength infrared (LWIR) (~8μm) detectors. To study buried QDs by X-STM, the sample has to be cleaved and measured in Ultra High Vacuum (UHV). In order to do this, a cleaving apparatus was built and installed on an STM system. A sample preparation methodology was worked out in order to make the samples ready for cleaving. An easy method for finding the QDs with the X-STM was also developed. Measurements resulted in a number of atomically resolved images, revealing the QD layer morphology. Furthermore, larger images were captured in order to study growth defects. Because of the high dot density, at low resolution the QDs were perceived as quantum wells. It was only at atomic resolution that QDs could be resolved. The observed dot sizes ranged between ~3 nm (InSb) and ~8 nm (In _0,4 Ga _0,6 Sb) in diameter.