Intersubband and interminiband spectroscopy of doped and undoped CdS/ZnSe multiple quantum wells and superlattices

Abstract

In cubic CdS/ZnSe type-II heterostructures collective excitations have been studied using infrared spectroscopy. The CdS/ZnSe structures were grown by solid-source molecular-beam epitaxy on semi-insulating GaAs substrates. Highly n-type-doped multiple-quantum-well and superlattice samples show strong intersubband and interminiband absorption in the midinfrared. The validity of the polarization selection rule is verified experimentally. The CdS/ZnSe conduction band offset is determined using a combination of interband and intersubband spectroscopy. Measured transition energies agree well to model calculations if many-body effects and band nonparabolicity are included. Intensity-dependent pump and probe measurements on doped and undoped samples reveal a fast increase of the photoinduced absorption signal at low pump intensities. At high pump intensities the absorption signal saturates. This behavior is explained by the existence of a subgroup of long-lived photogenerated electron-hole pairs. An observed redshift of the photoinduced interminiband transitions is explained by filling of the lowest miniband. The effective electron mass of cubic CdS is determined from thick films using infrared reflection spectroscopy.

Thermal annealing effects on intersubband transitions in (CdS∕ZnSe)∕BeTe quantum wells

“…The recent development of II-VI low-dimension structures has opened up the application of II-VI materials in the mid-or near-infrared ͑IR͒ spectral region. [5][6][7][8][9] The ͑CdS / ZnSe͒ / BeTe QWs reported in this letter have a type-II band alignment with a huge conduction band offset of 3.1 eV. 10 Most recently, we have observed the ISB-T down to ϳ1.5 m in this structure.…”

“…2͑a͔͒. The reduction of conduction band offset 5,13 together with the change of effective well thicknesses caused by the interdiffusion result in the shift of ISB absorption to the lower energy ͑longer wavelength͒ ͓Fig. 2͑b͔͒.…”

“…Figure 1͑a͒ shows the ISB absorption spectra of the asgrown samples, obtained by taking the -log of the ratio of transmittance of p-to s-polarized light. 2,5,6 The linewidths of the absorption peaks expressed in term of full width at half maximum ͑FWHM͒ are relatively narrow ͑⌬E / E p ϳ 10% -13% ͒. Upon annealing, the absorption peak position, intensity, and linewidth all change with the annealing temperature.…”

Growth and properties of wide bandgap MgSe/ZnxCd1−xSe multiple quantum wells for intersubband devices operating at short wavelengths

“…However, the fundamental aspect of p-type doping is still in severe challenge because of strong self-compensation in II-VI wide bandgap semiconductors. The recent development of II-VI CdS/ZnSe [1], (CdS/ZnSe)/BeTe [2], and ZnCdSe/ZnCdMgSe [3] quantum wells (QWs) has opened up application in mid-and near-infrared (IR) region using the intersubband (ISB) transitions within the conduction band of the QW, i.e., unipolar devices such as IR photodetectors, quantum cascade lasers (QCL), as well as ultrafast all-optical switches (UOS). Previously, it has been proposed that the II-VI-based QWs are the promising candidates for UOS at near-IR wavelength region due to the enhanced electron-phonon interaction [2].…”

Photoluminescence characterization of cubic CdS epilayers

“…Some research on cubic CdS optical properties [6][7][8][9], free excitons by photoluminescence (PL), and reflection [10-13] has been reported. Studies have also been carried out to grow cubic CdS-based low-dimensional quantum structures for opto-electronic devices [14]. Recently, we studied the room-temperature energy gap and the binding energy of the free exciton by absorption and PL [15,16].…”