Type I–type II band alignment of a GaAsSb/InAs/GaAs quantum dot heterostructure influenced by dot size and strain-reducing layer composition

MOVPE prepared InAs/GaAs quantum dots covered by GaAsSb layer with long wavelength emission at 1.8µm

“…One of the most important and more influencing factors of wavelength prolongation is the introduction of GaAsSb SRL. As known from previous research [1][2][3], the high amount of antimony in GaAsSb SRL causes the PL wavelength redshift. There are two reasons for such behavior.…”

“…HRTEM observations revealed the lensshaped morphology of the overgrown InAs QDs exhibiting a size of about 5 nm in height and 15 nm in width at the base. Their size does not significantly differ from the usual size of InAs QDs in samples prepared in our laboratory by MOVPE under similar growth conditions [3,5]. The cross-section HRTEM image of Fig.…”

“…Also, the sample is type II heterostructure because of the high concentration of Sb atoms in GaAsSb. Usually, the type I/type II transition occurs for approximately 15% of Sb atoms (it may vary by 1-2% depending on the QD size [3]) and the concentration for our sample is around 30%. The type II heterostructure evinces longer PL wavelength with decreased intensity as explained above.…”

“…Second the lattice parameter of GaAsSb is more similar to the lattice constant of InAs in comparison with GaAs, which ensures strain relaxation inside QD in comparison with covering directly by GaAs. Depending on the amount of Sb in GaAsSb SRL, the band alignment can be type I or type II; the transition occurs for approximately 14% of Sb [2], but it is also slightly dependent on the QD size [3]. In the type II heterostructure, electrons are confined in InAs QDs and holes in GaAsSb SRL.…”

Growth and properties of AIIIBV QD structures for intermediate band solar cells

“…The graded concentration of Sb in the reactor and in the GaAsSb layer achieved by this method was confirmed by RAS during the growth and by the HRTEM measurement of prepared structures [8]. The average Sb concentration in SRLs of samples I is lower than in samples D, however, both types of samples have the type II band alignment between QDs and SRL, which was proved by the PL measurement [9]. During the 15 s growth interruption, in case of samples D1, D5 and I1, I5, the H 2 /tBAs flow was changed from 0.5 to 2.05 ml/min and from 5 to 2.72 respectively.…”