Monolayer thickness fluctuations in infrared photoluminescence for [211]-oriented HgTe-CdTe superlattices

Abstract

We report the observation of multiple photoluminescence peaks due to monolayer thickness fluctuations in HgTe-CdTe superlattices. The spectra for seven different [211]-oriented superlattices with band gaps varying from 133 to 495 meV exhibit double peaks, and in nearly all cases the energy splitting corresponds to a difference of ≊1.5 ML in the quantum well thickness.

Mechanisms of infrared photoluminescence in HgTe/HgCdTe superlattice

“…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.…”

“…7,14,55 The multiple PL peaks with the peak-separation of at least 14 meV and the FWHM of about 25 meV at 77 K were ascribed solely to the effect of a 1.5 ML thickness fluctuation of the QW layers. 14 The single PL peak was considered to contain a shoulder or other substructure that could not be resolved 55 due to the restriction of spectral resolution of the PL measurements.…”

“…11,12 Unfortunately, the growth of the SL and accurate control of the layer thickness are of particular tricky, and the quality of the SL is inevitably affected by the interfacial effects of, e.g., chemical interdiffusion 13 and layer thickness fluctuation. 14,15 Among numerous optical studies of HgTe/CdTe SLs was photoluminescence (PL) very active, by which the thickness fluctuation, 14 valenceband structure, [16][17][18] and minibands 7 were investigated separately. For the PL measurements in the infrared spectral region beyond about 4 lm, continuous-scan Fourier transform infrared (FTIR) spectrometer-based doublemodulation PL techniques were employed to eliminate strong background thermal emission.…”

“…23 The situation even gets worse when extremely weak PL signal is to be detected but only photoconductive (PC) HgCdTe detector available in the far-infrared spectral range of 12-20 lm, due partly to the two orders of magnitude performance degradation of the HgCdTe detector in this spectral range 24 relative to the counterpart of, e.g., InSb detector in the shorter wavelength spectral region. 23 To clarify the mechanisms of whether the PL signal simply reflecting the layer thickness fluctuation 14 or solely correlating to the band-to-band transition, quantitative curve-fitting analysis of the PL spectra in a wide temperature range 7 is highly demanded, for which PL spectra with reasonable SNR and spectral resolution are very crucial.…”

Photoluminescence ofHgTe∕Hg1−xCdxTesuperlattices and a study of min

“…The PL double peaks observed by Meyer et al 6 in HgTe/ Hg 1−x Cd x Te SL's were shown to be due to monolayer fluctuations in the layers. In this investigation, the results of optical absorption experiments on HgTe/ Hg 1−x Cd x Te superlattice are compared with those of PL for temperatures between 5 and 300 K. Experimental evidence of minibands, i.e., two closely spaced peaks or a peak with a pronounced shoulder, have been observed in absorption spectra and compared to theoretical calculations.…”