Large blueshift of the band gap of GaAsSb∕AlSb quantum wells with ion implantation
Applied Physics Letters
We describe studies of intermixing in GaAsSb/ AlSb quantum wells with 18.8% and 31% arsenic, grown on GaSb substrates. Samples were implanted with a 1 ϫ 10 13 cm −2 dose of 330 keV boron ions and annealed. The band gap for the samples was determined from photoluminescence. The maximum blueshift of the band gap was 141 nm ͑86 meV͒ for the quantum wells with 18.8% arsenic and 198 nm ͑124 meV͒ for the quantum wells with 31% arsenic. The blueshifts are attributed to interdiffusion of both group-III
... n of both group-III and group-V constituents. Photoluminescence strength generally increased with annealing temperature. Realization of complex photonic integrated circuits often requires spatially selective control of the optical properties of materials. Passive devices are typically transparent while active devices have absorption or gain. A promising approach to selective control of optical properties is semiconductor band-gap modification by ion-induced quantum well intermixing. 1-3 Semiconductor quantum wells are implanted with ions and then annealed. The constituents of the quantum wells diffuse during the annealing of the ion-damage material, which is also repaired during the annealing process. Diffusion rounds the confinement profile of the quantum well causing a change in band gap, usually a blueshift. A large blueshift is particularly desirable for applications like coarse wavelength division multiplexing (CWDM) 4 where a broad range of optical wavelengths is used. For semiconductor photonic devices operating in the 1270-1610 nm range (the CWDM band), InP-based materials are typically employed. Skogen et al. demonstrated a band-gap shift for InGaAs/ InP quantum wells of 130 nm in the CWDM band by implantation of a 5 ϫ 10 14 cm −2 dose 100 keV phosphorus ions. 5 Han et al. demonstrated a 132 nm band-gap shift in the CWDM band for InGaAsP / InP quantum wells by implantation of a 9 ϫ 10 13 cm −2 dose of 2 MeV ions. 6 Here we report very large band-gap shifts of up to 198 nm in the CWDM band by implantation of boron in GaAsSb/ AlSb quantum wells grown on GaSb substrates. Figure 1 shows the cross section for the two types of multiple quantum well samples used in this study. The first type had 60 GaAsSb wells of width 51 Å with an arsenic fraction of 18.8%. The second type had 60 GaAsSb wells of width 45 Å with an arsenic fraction of 31%. To suppress dislocations, the thickness of the AlSb barriers (80 and 85 Å) was adjusted so that the product of thickness and strain was approximately the same as for the GaAsSb wells, but of opposite sign. Well width and composition were chosen to produce an absorption edge near 1.5 m (Fig. 2) ; and photoluminescence for as-grown samples had peaks at 1498 and 1508 nm for the 18.8% and 31% samples, respectively. Both multiple quantum well structures were grown on top of a 5-period AlSb/ Al 0.32 Ga 0.68 Sb Bragg reflector, included for separate reflectance measurements that are not described here. 7,8 A 1000 Å GaSb buffer preceded Bragg reflectors.