Photoluminescence ofHgTe∕Hg1−xCdxTesuperlattices and a study of min

Abstract

It has been demonstrated that two closely spaced peaks in the infrared absorption spectra of several HgTe/ Hg 1−x Cd x Te͑112͒B superlattices ͑SL's͒ are due to the H1-E1 intersubband transition at the center of the Brillouin zone and the zone boundary. The miniband width agrees well with ͑8 ϫ 8 k · p͒ calculations. The intersubband transition energies of SL's with both large and small miniband widths have been compared with photoluminescence ͑PL͒ spectra over a temperature range of 5 -300 K for a number of superlattices with band gaps between 100 and 510 meV at 5 K. The band gap as determined from the peak of the first derivative of the absorption coefficient, i.e., the corresponding intersubband transition energy, agrees well with the PL peak energy. With increasing temperature the PL peak energy increases faster than the band gap by a range of factors given by 0.25-0.75k B T, however, which are well within the width of the thermally broadened PL peaks.

Mechanisms of infrared photoluminescence in HgTe/HgCdTe superlattice

“…The ME component may be due to the first electron subband level (E1) to the first heavy-hole subband level (H1) transition. 7 The LE component is related to the localization effect introduced by interfacial roughness, defects, and/or QW layer-thickness fluctuation. 15 The defects result in band-tail states like, e.g., in GaNAs/GaAs quantum wells.…”

“…47,48 The thickness fluctuation is at a level of less than 1 monolayer (ML), 14 which is very close to that previously derived by absorption measurements for a similar HgTe/ HgCdTe SL. 7 The HE component may be a signature for the inhomogeneous chemical intermixing across the HgTe and HgCdTe interfaces 49,50 and the effect of Brillouin-zone boundary. 7 Interdiffusion was found to occur in the HgTe/CdTe SLs grown at temperatures above 180 C, 51,52 which would enhance the band gap at the interface relative to the abrupt HgTe/CdTe SLs.…”

“…7 The HE component may be a signature for the inhomogeneous chemical intermixing across the HgTe and HgCdTe interfaces 49,50 and the effect of Brillouin-zone boundary. 7 Interdiffusion was found to occur in the HgTe/CdTe SLs grown at temperatures above 180 C, 51,52 which would enhance the band gap at the interface relative to the abrupt HgTe/CdTe SLs. 13,49 Theoretical analysis of AlAs/GaAs SLs also suggested that chemical intermixing across the interface shifted significantly the SL energy levels.…”

“…53 Furthermore, the energy difference between the center and the boundary of the Brillouin zone is about 20 meV as suggested for the similar HgTe/HgCdTe SLs. 7 The LO phonon scattering may be enhanced at higher temperatures due to alloy fluctuation and the boundary states, giving rise to a relatively quicker blueshift and broadening while quenching of the integral intensity to the corresponding PL component.…”

“…[2][3][4][5][6][7][8] Recently, new attention has been drawn to the inverted HgTe/CdTe quantum wells (QWs) due to the characteristic of topological insulator. Analysis predicted that the invertion of the band alignment occurs when the HgTe layer is thicker than 6.3 nm, 9 which was proved ideal for the observation of quantum spin Hall insulator phase.…”