T.D. Das

Effect of post-growth anneal on the photoluminescence properties of GaSbBi

The effect of post-growth anneal on the photoluminescence (PL) properties of GaSbBi layers, grown by liquid phase epitaxy, is investigated. It is observed that annealing for temperatures up to 650 °C increases the PL intensity and decreases the PL peak width indicating an improvement in the crystalline quality of the layer. A second peak at 0.72 eV, observed in GaSbBi only, is totally removed by annealing, suggesting that the peak is related to emission from Bi-related antisite defects. A red shift of up to 9 meV is also observed for the band edge emission peak as a result of anneal.

Calculation of Direct E0 Energy Gaps for III–V–Bi Alloys Using Quantum Dielectric Theory

A mathematical model based on Quantum Dielectric Theory has been used to calculate the direct E0 energy gaps of bismuth containing ternary alloys. The variation of E0 with x for In Sb1–xBix and GaSb1–xBix are in good agreement with the experimental results. The composition dependence of E0 at different temperatures is also found out for some other ternary alloys like InPBi and AlSbBi.

Properties of GaAsN layers grown from melt containing Li3N as flux for enhancing nitrogen dissolution

Dilute GaAsN layers are grown by the liquid phase epitaxy technique from a GaAs + Ga + GaN melt with up to 2 mol% Li3N added to the same to act as a flux to promote nitrogen dissolution in Ga. X-ray diffraction study indicates a nitrogen content of 0.9 at.% in the material. 10 K photoluminescence measurements indicate a band gap reduction of 130 meV in the as-grown layers which increases to 150 meV after a high-temperature anneal. Energy dispersive x-ray measurements indicate incorporation of Li in the material and local vibrational modes related to both nitrogen and Li are observed through Raman spectroscopy. Furthermore, a photoluminescence peak at 1.33 eV is suggested to be due to Li.

Hall mobility and electron trap density in GaAsN grown by liquid phase epitaxy

The Hall mobility of GaAsN layers grown by liquid phase epitaxy (LPE) is studied as a function of the nitrogen content in the material. It is observed that the parameter decreases with increasing nitrogen in the layer, in agreement with earlier theoretical predictions assuming scattering of electrons in nitrogen-related defects. It is also found that the decrease in mobility is accompanied by a corresponding increase in the density of electron traps, believed to originate from different configurations of nitrogen defect centers. The observation clearly suggests that nitrogen-related defects are responsible for lowering the mobility in LPE-grown GaAsN.

Calculation of Valence Band Structure of GaSb 1−x Bi x Using Valence Band Anticrossing Model in the Dilute Bi Regime

Valence Band anticrossing model is used to estimate the reduction in band gap and increase in spin-orbit splitting energy for GaSb1−xBix. Interaction of the heavy hole (HH), light hole (LH) and the SO bands of GaSb with the Bi related impurity level causes restructuring of the valence band structure of the III-V-bismide. While the HH/LH sub band moves in the upward direction, SO band moves in the downward direction to result in a significant increase in spin orbit splitting energy. The decrease in band gap and the increase in the splitting energy results in the formation of ∆SO > EBi regime which suppress the loss mechanisms such as Auger recombination and Intervalence Band Absorption in GaSb based LASERS and photodetectors.

Effect of Bismuth Incorporation on the Growth Kinetics and Valence Band Structure for InP1−xBix Grown Using Liquid Phase Epitaxy

A mathematical model based on the one dimensional diffusive transport of bismuth atoms has been used to study the concentration profile of the bismuth atoms during the liquid phase epitaxial growth of InPBi. This model is used to determine the growth kinetics at equally spaced layers in the proximity of the grown epitaxial interface. Various growth parameters such as growth temperature, melt supercooling and the continuous cooling ramp applied during growth have been optimized to find out the suitable conditions of growth. The thickness of the epitaxial layers as a function time is also estimated. Valence Band anticrossing (VBAC) model is used to determine the reduction in band gap and increase in spin-orbit splitting energy for InP1−xBix. The valence band structure of InPBi is modified due to the interaction of the Bi related impurity levels with the light hole (LH), heavy hole (HH) and spin-orbit split-off (SO) sub bands. A 12 × 12 Hamiltonian is solved to find out the valence band structure of InPBi in the direction.

Bi incorporation in GaSbBi films grown by liquid phase epitaxy

We present here the Bi incorporation properties of GaSbBi layers grown by liquid phase epitaxy technique. Secondary ion mass spectroscopy technique indicates that Bi is distributed uniformly along the depth of the layer with slowly decreasing concentration away from the surface. Room temperature optical absorption measurements show a band gap lowering of 25 meV for a layer grown from a melt containing 1 at% Bi.

Physical and electrical properties of of dilute GaAsN and InAsN layers grown by liquid phase epitaxy

We have grown GaAsN and InAsN layers by liquid phase epitaxy technique and measured their physical and electrical properties. Hall electron mobility of GaAsN layers is found to decrease as the nitrogen concentration in the material is increased. This corresponds to a simultaneous increase in the concentration of a nitrogen related 0.7 eV electron trap, measured by low temperature photocapacitance technique. This result indicates that the (N-N)as defect, which is believed to be the origin of the electron trap, is partly responsible for the decrease in mobility. InAsN layers have been characterized by energy dispersive X-ray and high resolution X-ray diffraction measurements and the presence of nitrogen in the material has been confirmed.