Formation and phase transformation of Bi-containing QD-like clusters in annealed GaAsBi

Abstract

We report the formation and phase transformation of Bi-containing clusters in GaAs(1-x)Bi(x) epilayers upon annealing. The GaAs(1-x)Bi(x) layers were grown by molecular beam epitaxy under low (220 °C) and high (315 °C) temperatures and subsequently annealed using different temperatures and annealing times. Bi-containing clusters were identified only in the annealed samples that were grown at low temperature, revealing a relatively homogeneous size distribution. Depending on the annealing temperature and duration, the clusters show different sizes ranging from 5 to 20 nm, as well as different crystallographic phase, being coherently strained zincblende GaAs(1-x)Bi(x) (zb Bi-rich Ga(As, Bi)) clusters or rhombohedral pure Bi (rh-Bi) clusters. We found that: (1) the formation of the zb Bi-rich Ga(As, Bi) clusters is driven by the intrinsic tendency of the alloy to phase separately and is mediated by the native point defects present in the low temperature grown epilayers; (2) the phase transformation from zb Bi-rich Ga(As, Bi) to rh-Bi nucleates in zincblende {111} planes and grows until total consumption of Bi in the GaAs matrix. We propose a model accounting for the formation and phase transformation of Bi-containing clusters in this system. Furthermore, our study reveals the possibility to realize self-organized zb Bi-rich Ga(As, Bi) clusters that can exhibit QD-like features.

Investigation of MBE-grown InAs1−Bi alloys and Bi-mediated type-II superlattices by transmission electron microscopy

“…EDX analysis performed on various droplet positions indicates that the droplet consists predominantly of Bi. In comparison, Bi-rich zincblende Ga(As, Bi) clusters and rhombohedral Bi clusters were reported for GaAsBi after annealing [21], and InBi clusters with distorted PbO structure were reported in InAsBi [22]. Such phase separation is attributed to the difficulties associated with Bi incorporation.…”

Novel Dilute Bismide, Epitaxy, Physical Properties and Device Application

“…They found that Bi atoms segregated to form anisotropic microstructures like pannikins [107]. Luna et al found lateral composition modulations (LCMs) by means of transmission electron microscope (TEM) [110]. The TEM images show that Bi atoms segregate to form quasi-periodical nano-columns along the growth direction.…”

“…The TEM images show that Bi atoms segregate to form quasi-periodical nano-columns along the growth direction. Wu et al also used TEM to observe phase segregation phenomenon in GaAsBi during annealing and found Bi clusters [110]. The phase was found to transform from ZB Bi-rich to rhombohedral-Bi in {111} continually until all the Bi atoms were consumed in the matrix.…”

“…Still, In-V-Bi compounds could be successfully grown with InBi in ZB structure under a proper growth condition. Wu et al studied structure of Bi clusters in annealed GaAsBi films [110]. Due to phase separation, Bi-containing clusters are easily formed and the initial Bi rich ZB Ga(As,Bi) could transform to rhombohedral Bi clusters in ZB {111} planes until complete depletion of Bi atoms in the GaAs matrix.…”

Understanding and reducing deleterious defects in the metastable alloy GaAsBi

“…Thermal annealing has been used to reduce the defects, but the incorporated Bi atoms often segregate and form Bi-rich clusters. 13 These defect-related issues have become a bottleneck in the successful applications of GaAsBi. For instance, to date, GaAsBi-based laser diodes require a threshold current density (2-10 kA cm − 2 ) 6,[14][15][16] that is approximately an order of magnitude higher than that of typical InGaAs-based laser diodes (0.2-0.5 kA cm − 2 ).…”