Energy band structure tailoring of vertically aligned InAs/GaAsSb quantum dot structure for intermediate-band solar cell application by thermal annealing process

Abstract

This study presents an band-alignment tailoring of a vertically aligned InAs/GaAs(Sb) quantum dot (QD) structure and the extension of the carrier lifetime therein by rapid thermal annealing (RTA). Arrhenius analysis indicates a larger activation energy and thermal stability that results from the suppression of In-Ga intermixing and preservation of the QD heterostructure in an annealed vertically aligned InAs/GaAsSb QD structure. Power-dependent and time-resolved photoluminescence were utilized to demonstrate the extended carrier lifetime from 4.7 to 9.4 ns and elucidate the mechanisms of the antimony aggregation resulting in a band-alignment tailoring from straddling to staggered gap after the RTA process. The significant extension in the carrier lifetime of the columnar InAs/GaAsSb dot structure make the great potential in improving QD intermediate-band solar cell application.

Capping vertically aligned InGaAs/GaAs(Sb) quantum dots with a AlGaAsSb spacer layer in intermediate‐band solar cell devices

“…The state‐filling effect can be accounted by the particular characteristic of three‐dimensional carrier confinement in a QD structure that is demonstrated by the PDPL measurements. The observation of reduced intersublevel spacing energies in samples A and B indicates a transition of the QDs to a quantum‐well‐like structure leading to the reduced carrier confinement ascribed to the In–Ga intermixing . However, the appearance of additional excited states and the enlarged intersublevel spacing energy of 50 meV in sample C verify the improved dot‐size uniformity and the preservation of the QD heterostructure with reduced In–Ga intermixing for the GaAsSb‐capped QDs, as shown in Figures and .…”

“…For a columnar dot structure, the accumulated compressive strain is caused by the InGaAs QDs, inducing the selective growth of successive QD layers that are vertically aligned on top of the underlying QDs. This strain‐field distribution contributed to the aggregation of the Sb atoms toward the top region of the QDs because of the strain energy selectivity .…”

“…Previous studies have shown that inserting a GaAsSb layer into an In(Ga)As/GaAs QD system can increase the dot density and reduce the coalescence dots because of the reduced surface energy by Sb surfactant . Furthermore, GaAsSb‐capped QDs can suppress In–Ga intermixing in QD systems and preserve the QD heterostructure, ensuring high‐temperature stability during subsequent epitaxial layer growth at high temperatures . Therefore, the material characteristics, crystal quality, and optoelectronic properties of InGaAs/GaAsSb QD devices were improved .…”

Tailoring Energy Band Alignment of Vertically Aligned InGaAs Quantum Dots Capped with GaAs(Sb)/AlGaAsSb Composite Structure after Thermal Annealing Treatment

“…The GaAsSb capping layer with a large lattice constant served as a strain-reduction layer in the InGaAs QD structure, enabling the stress field above the QDs to be modified and yielding the uniform stress distribution under each dot layer, and thus the uniform dot-size distribution was observed in sample C. Moreover, the observed increased dot density in sample C was probably related to the surfactant effect of Sb, which may have diffused from the underlying GaAsSb/AlGaAsSb layers when a thin layer of GaAs deposited at high temperature. The surfactant effect of Sb is expected to reduce the surface migration of group III adatoms, increasing the dot density compared to the QDs without the GaAsSb overgrown layer in samples A and B. ,,, …”

Temperature-dependent Luminescence Properties of Digital-alloy In(Ga1−zAlz)As

“…Temperature-(T-) dependent optical processes give rise to various thermal dynamics of carriers in semiconductors such as carrier redistribution between energy states and/or carrier escape from active region to barrier [11,12] and can calculate the interband energy spacing by analyzing the Tdependent integrated photoluminescence (PL) intensity [13]. In this paper, the luminescence properties of digital-alloy In(Ga 1-z Al z )As grown by MBE have been investigated by using a T-dependent PL as a function of composition z in digital-alloy (In 0.53 Ga 0.47 As) 1-z /(In 0.52 Al 0.48 As) z (z = 0.4, 0.6, and 0.8).…”