The use of synchrotron radiation techniques in the characterization of strained semiconductor heterostructures and thin films

The present article describes a novel application of capacitance–voltage measurements to determine simultaneously the band discontinuities (ΔEV, ΔEC) and interface charge density (σ) of heterojunctions. The method, which we refer to as C–V matching, complements the most versatile C–V profiling technique proposed by Kroemer and successfully applied by others. In contrast to the C–V profiling which is limited to isotype heterojunctions, the new method is applicable to p-n heterojunctions as well. The methodology is based on three cardinal equations which are not controversial—the lineup of the bands relative to the common Fermi level (at equilibrium) or the quasi-Fermi levels (when voltage is applied), the charge neutrality and the expression for the total capacitance of the heterostructure. The three equations are formulated for equilibrium as well as nonequilibrium conditions, using quasi-Fermi levels and the quasi-equilibrium approximation. The three cardinal equations are defined by the two constant (al...

Measurement of band offsets and interface charges by the C–V matching method

Evidence of a deep donor in CdTe

Electrochemical growth and characterization of manganese telluride thin films

We have investigated the valence band offset (ΔE VBO ) of the molecular beam epitaxially grown heterostructure HgTe/CdTe(001) by k-resolved ultraviolet (UPS) and X-ray (XPS) photoemission. Our angle-dependent UPS measurements at two different photon energies demonstrate that the dispersion of the valence band (VB) must be checked carefully in order to find the true position of the VB maximum in the Brillouin zone. With this information the valence band discontinuity was determined as (0.53 ± 0.03) eV, which is different from previously found photoemission values but now agrees well with magneto-optical investigations. In addition, we have determined the energy gap of CdTe(001) and HgTe(001) by a combination of UV and inverse photoemission. The energy gap of CdTe is determined to (1.57 ± 0.06) eV and that for HgTe as (0.0 ± 0.06) eV. We therefore conclude that HgTe is a semi-metal with inverted band structure in agreement with other results.

Band Discontinuity and Band Gap of MBE Grown HgTe/CdTe(001) Heterointerfaces Studied by k‐Resolved Photoemission and Inverse Photoemission

We report here that reconstruction on (100), (111)A, and (111)B CdTe surfaces is either c(2\ifmmode\times\else\texttimes\fi{}2), (2\ifmmode\times\else\texttimes\fi{}2), and (1\ifmmode\times\else\texttimes\fi{}1) or (2\ifmmode\times\else\texttimes\fi{}1), (1\ifmmode\times\else\texttimes\fi{}1), and (1\ifmmode\times\else\texttimes\fi{}1) when they are Cd or Te stabilized, respectively. There is a mixed region between Cd and Te stabilization in which the reflected high-energy electron-diffraction (RHEED) patterns contain characteristics of both Cd- and Te-stabilized surfaces. We have also found that the Cd-to-Te ratio of the x-ray photoelectron intensities of their 3${\mathit{d}}_{3/2}$ core levels is about 20% larger for a Cd-stabilized (111)A, (111)B, or (100) CdTe surface than for a Te-stabilized one. According to a simple model calculation, which was normalized by means of the photoelectron intensity ratio of a Cd-stabilized (111)A and a Te-stabilized (111)B CdTe surface, the experimental data for CdTe surfaces can be explained by a linear dependence of the photoelectron-intensity ratio on the fraction of Cd in the uppermost monatomic layer. This surface composition can be correlated with the surface structure, i.e., the corresponding RHEED patterns. This correlation can in turn be employed to determine Te and Cd evaporation rates. The Te reevaporation rate is increasingly slower for the Te-stabilized (111)A, (111)B, and (100) surfaces, while the opposite is true for Cd from Cd-stabilized (111)A and (111)B surfaces. In addition, Te is much more easily evaporated from all the investigated surfaces than is Cd, if the substrate is kept at normal molecular-beam-epitaxy growth temperatures ranging from 200 \ifmmode^\circ\else\textdegree\fi{}C to 300 \ifmmode^\circ\else\textdegree\fi{}C.

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Correlation of the Cd-to-Te ratio on CdTe surfaces with the surface structure

The authors have investigated the valence band offset ( Delta EV) of the CdTe-HgTe heterojunction for three orientations, (100), (110) and (111)B, using in situ X-ray photoelectron spectroscopy. The difference in energy between the Cd 4d and Hg 5d5/2 core levels, Delta ECL, and consequently Delta EV was found to be independent of surface orientation and the surface structure immediately prior to growth of the uppermost layer. Delta EV was found to be 0.37+or-0.07 eV.

/pdf/the-orientation-independence-of-the-cdte-hgte-valence-band-5djpo4zr5d.pdf

The orientation independence of the CdTe-HgTe valence band offset as determined by x-ray photoelectron spectroscopy

Hg1-xCdxTe is an important material for infrared device technology. Despite a variety of investigations on molecular beam epitaxially (MBE) grown Hg-based superlattices and modulation-doped structures, little attention has been paid to the study of the photoluminescence properties of the constituent materials. The authors report on a systematic study of infrared photoluminescene on Hg1-xCdxTe layers grown by MBE. The Fourier transform photoluminescence of Hg1-xCdxTe layers with 0.25<x<0.93 grown on (110) and (211) GaAs was investigated in the spectral range from 01 eV to 1.5 eV. Emission lines were observed with a full width at half maximum down to 15 meV. Photoluminescence and transmission properties are compared over the temperature range from 4.2 K to 300 K. The possible influence of Burstein-Moss shift, impurity bands and exponential band tails are discussed. Photoluminescence at high temperatures originates from band-to-band transitions. However, low temperature photoluminescence can be attributed either to impurity bands or to additional states due to band tails.

/pdf/infrared-photoluminescence-on-molecular-beam-epitaxially-4xe4s6trqr.pdf

Infrared photoluminescence on molecular beam epitaxially grown Hg1-xCdxTe layers

Photoassisted MBE growth of doped CdTe and CdMnTe thin films and their characterization

The molecular beam epitaxially growth of (001) Hg1-xCdxTe-HgTe superlattices has been systematically investigated. The well width as well as the period were determined directly by X-ray diffraction. This was accomplished for the well width by exploiting the high reflectivity from HgTe and the low reflectivity from CdTe for the (002) Bragg reflection. Knowing the well and barrier thicknesses we have been able to set an upper limit on the average composition of the barriers, xb, by annealing the superlattice and then measuring the composition of the resulting alloy. xb was shown to decrease exponentially with decreasing barrier width. xb is appreciably smaller in narrow barriers due to the increased significance of interdiffusion in the Hg1-xCdxTe/HgTe interface in narrow barriers. The IR photoluminescence was investigated at temperatures from 4.2 to 300 K. Pronounced photoluminescence was observed for all superlattices in this temperature range.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

/pdf/molecular-beam-epitaxial-growth-and-characterization-of-001-2mhfdlhw8x.pdf

M. M. Kraus

Papers

Correlation of the Cd-to-Te ratio on CdTe surfaces with the surface structure

The orientation independence of the CdTe-HgTe valence band offset as determined by x-ray photoelectron spectroscopy

Infrared photoluminescence on molecular beam epitaxially grown Hg1-xCdxTe layers

Photoassisted MBE growth of doped CdTe and CdMnTe thin films and their characterization

Molecular beam epitaxial growth and characterization of (001) Hg1-xCdxTe-HgTe superlattices