Pallavi Patil

GaAsBi/GaAs multi-quantum well LED grown by molecular beam epitaxy using a two-substrate-temperature technique

We report a GaAs0.96Bi0.04/GaAs multiple quantum well (MQW) light emitting diode (LED) grown by molecular beam epitaxy using a two-substrate-temperature (TST) technique. In particular, the QWs and the barriers in the intrinsic region were grown at the different temperatures of [Formula: see text] = 350 °C and [Formula: see text] respectively. Investigations of the microstructure using transmission electron microscopy (TEM) reveal homogeneous MQWs free of extended defects. Furthermore, the local determination of the Bi distribution profile across the MQWs region using TEM techniques confirm the uniform Bi distribution, while revealing a slightly chemically graded GaAs-on-GaAsBi interface due to Bi surface segregation. Despite this small broadening, we found that Bi segregation is significantly reduced (up to 18% reduction) compared to previous reports on Bi segregation in GaAsBi/GaAs MQWs. Hence, the TST procedure proves as a very efficient method to reduce Bi segregation and thus increase the quality of the layers and interfaces. These improvements positively reflect in the optical properties. Room temperature photoluminescence and electroluminescence (EL) at 1.23 μm emission wavelength are successfully demonstrated using TST MQWs containing less Bi content than in previous reports. Finally, LED fabricated using the present TST technique show current-voltage (I-V) curves with a forward voltage of 3.3 V at an injection current of 130 mA under 1.0 kA cm-2 current excitation. These results not only demonstrate that TST technique provides optical device quality GaAsBi/GaAs MQWs but highlight the relevance of TST-based growth techniques on the fabrication of future heterostructure devices based on dilute bismides.

Statistical investigations on the development of GaAs/GaAsBi core-multi shell nanowires

We statistically investigate the development of GaAs/GaAsBi core-multi shell nanowires. The wire diameters were precisely controlled by adjusting the growth procedure. The wire having GaAs/GaAsBi core-shell nanowire, presumably having Bi concentration less than 1%, shows straight sidewall with sphere-shaped structure on the tip. The diameter was 250 nm ± 32 nm. GaAs/GaAs0.98Bi0.02/GaAs core-multi shell nanowire showed characteristic rough surface. The diameter was 376 nm ± 33 nm. In contrast, when we grew GaAs nanowire with identical growth conditions of the multi shell nanowires, they showed straight sidewall with its diameter described by 375 nm ± 30 nm. The results shows we can control the diameter and the shell structures of the wires. Further, specific surface roughening occurs by the introduction of Bi on the outer shells.

MBE growth and characterization of strained GaAsBi/GaAs MQWs

Eleven periods of highly strained GaAsBi/GaAs MQWs were grown on GaAs (100) substrates by MBE to study Bi incorporation dependent on As₄ flux. We obtained largest Bi incorporation at As₄ BEP of 1.0 × 10^-5 mbar. From analysis of incorporated Bi by HRXRD, the growth mode transfer is suggested at smaller or larger regime of an As₄ BEP of 1.0 × 10^-5 mbar. In the smaller regime, the Bi incorporation was enhanced with increase of As BEP. On other hand, Bi incorporation was almost constant at the higher regime. The AFM image shows that the sample grown at As₄ BEP of 1.0 × 10^-5 mbar has a smooth surface region and island like region, overall rms roughness is 6.8 nm. The PL obtained at 10 K showed a clear redshift of peak positions reflecting incorporation of Bi. At largest Bi concentration of 3.8%, we observe a peak emitting over 1100 nm at 10K for MQWs.