Epitaxial phases of high Bi content GaSbBi alloys

Abstract

GaSbBi alloys have recently emerged as attractive materials for mid-infrared optoelectronics owing to strong band gap reduction enabled by Bi incorporation into the GaSb matrix. The fundamental understanding of the epitaxial process required to demonstrate high quality crystals is in an early-developmental phase. From this perspective, we report on the key role played by the Sb/Ga flux ratio in controlling the structural quality and incorporation of high Bi content (up to 14.5 %-Bi), revealing three distinct epitaxial phases. The first phase (below stoichiometric Sb/Ga) exhibits Ga-Bi compound droplets, low crystal quality, and reduced Bi content. At the second phase (above stoichiometric Sb/Ga), the crystal exhibits smooth surfaces and excellent crystallinity with efficient Bi incorporation. The last phase corresponds to exceeding a Sb/Ga threshold that leads to reduced Bi incorporation, Bi droplets and degraded crystallinity. This threshold value that defines the optimal growth window is controlled by the temperature as well as the Bi/Ga ratio. Increasing temperature increases the threshold, albeit simultaneously reducing Bi incorporation. Conversely, increasing the Bi/Ga flux ratio increases Bi incorporation, while narrowing down and ultimately closing the window. This study provides a general framework enabling development of high quality GaSbBi heterostructures for emerging mid-infrared optoelectronics.

Influence of the Bismuth Content on the Optical Properties and Photoluminescence Decay Time in GaSbBi Films

“…Two samples with different bismuth atom concentrations, sample A5.8% and sample B8.0%, were investigated. Both samples were grown on 500 μm-thick (100) n-GaSb substrates using the same growth procedure as in our earlier work . In short, the growth is initiated by depositing a surface-smoothing 100 nm-thick GaSb layer at ∼500 °C, followed by a temperature ramp-down sequence to ∼300 °C, with both temperatures estimated via pyrometry.…”

“…The low temperature is required for Bi incorporation into the subsequently grown 150 nm-thick GaSbBi layer together with a low Sb-flux overpressure slightly above the stoichiometric 1:1 flux ratio. More details on the influence of growth conditions on Bi incorporation and the resulting structural properties of GaSbBi are presented elsewhere …”

“…Both samples were grown on 500 μm-thick (100) n-GaSb substrates using the same growth procedure as in our earlier work. 11 In short, the growth is initiated by depositing a surface-smoothing 100 nm-thick GaSb layer at ∼500 °C, followed by a temperature ramp-down sequence to ∼300 °C, with both temperatures estimated via pyrometry. The low temperature is required for Bi incorporation into the subsequently grown 150 nm-thick GaSbBi layer together with a low Sb-flux overpressure slightly above the stoichiometric 1:1 flux ratio.…”

“…Such properties make III–V Bi semiconductors attractive for optoelectronic devices operating in the near- and mid-infrared spectral ranges. However, the large size of the Bi atom and its nature to bond weakly to group III atoms makes it difficult to incorporate Bi into the III–V lattice, and thus Bi tends to segregate to the crystal growth surface and/or evaporate . A yet emerging alloy in the III–V Bi family is GaSbBi, which has attracted attention due to its potential applications in the mid-IR region.…”

“…However, the large size of the Bi atom and its nature to bond weakly to group III atoms makes it difficult to incorporate Bi into the III–V lattice, and thus Bi tends to segregate 10 to the crystal growth surface and/or evaporate. 11 A yet emerging alloy in the III–V Bi family is GaSbBi, which has attracted attention due to its potential applications in the mid-IR region. However, so far, most studies have focused on the growth and structural properties of the novel alloy, with only a few groups demonstrating in detail their optical properties.…”