From magnetotransport measurements it is generally believed that Hg-VI compounds show zero gap semiconducting behavior. Applying combined angle-resolved photoemission and inverse photoemission spectroscopy on HgSe(001) c͑2 3 2͒, we observe a positive fundamental gap of about 0.42 eV and a surface related state close to the Fermi level above the conduction band minimum. Following the results of this direct determination of the k-resolved band structure, previous experiments favoring zero gap models of Hg-VI compounds need to be reinterpreted. [S0031-9007 (97)03026-3] PACS numbers: 73.20.At, 79.60.BmBecause of its technological interest for electro-optical devices, the Zn and Cd containing II-VI compound semiconductors have been studied intensively over the past decade. The group of Hg containing II-VI compounds, however, has been scarcely investigated since its electronic structures were reported to reveal zero or even negative fundamental gaps with inverted band structures. Following results on a-Sn from Groves and Paul [1], the valence band maximum (VBM) was considered to be degenerate with the conduction band minimum (CBM) revealing G 8 symmetry. Early magnetotransport measurements measuring extremal cross sections of Fermi surfaces indeed found evidence for an inverted band structure in bulk HgSe [2-4] similar to those observed on HgTe [5] and b-HgS [6].Semiempirical band structure calculations for HgSe [7-9] and HgTe [7,8,10] fitting those data, consequently, show an inverted band structure with valence band widths of the order of 3.3-4.4 eV for HgSe and 3.6-4.8 eV for HgTe, respectively. Photoemission results on HgSe and HgTe [11][12][13][14][15], in contrast, exhibit larger valence band widths of about 5.0-5.8 eV. The experimental position of the Fermi level with respect to the VBM is of particular interest in order to distinguish between metallic and semiconducting band structures. It has, however, only been reported for HgTe(110) by Yu et al. [11]. They determined the Fermi level to be 0.59 eV above the VBM. Infrared absorption data [16,17] show two absorption edges around 0.4 and 0.2 eV photon energy which are interpreted as transitions from the two upper valence bands near G 8 and G 6 into the G 8 conduction band, leading to a fundamental energy gap of approximately 20.2 eV.The experimental results, together with the semiempirical band structure calculations reported so far, do not give a consistent picture of the band structure around the Fermi level of Mercury containing II-VI compounds. This can be attributed to the type of experiments giving only indirect information on band structures (optical and magnetotransport measurements) and theories fitting these data.In this Letter we take HgSe as the prototype material of Hg-VI compounds which, in addition, may be compared to the better-known narrow gap semiconductor InAs having a similar lattice constant. We report on direct measurements of the k-resolved occupied and unoccupied band structure around the Fermi level of HgSe(001) c͑2 3 2͒ by means of comb...
Angular-resolved photoemission measurements of the nonpolar ͑110͒-cleavage face of HgTe single crystals have been performed along the ⌺ line to determine details of the band structure near the valence band maximum ͑VBM͒. Three bands are observed between VBM and 1 eV binding energy, instead of the two observed for a positive energy gap semiconductor CdTe. Their energy separations and positions relative to the Fermi energy are investigated at the ⌫ point and at slightly off-normal emission, applying room and low temperature of 40 K. In contrast to the heavily debated results of HgSe ͓K.-U. Gawlik et al., Phys. Rev. Lett. 78, 3165 ͑1997͔͒ the clear observations for HgTe are consistent with the model of an inverted band structure, reflecting a semiconductor with a negative band gap.
Gawlik et al. Reply:The Comment [1] avoids the main point of our Letter [2], namely, that for HgSe there is no evidence for a bulk conduction band state crossing or touching the valence band maximum determined by photoemission spectroscopy excited with different photon energies. This is a fundamental criterion for a metallic band structure. Therefore, from our experimental data an inverted band structure model for HgSe is not supported.Furthermore, the discussion of quantized charge accumulation states as performed by the authors of the Comment has no relevance for the conclusion of HgSe being a positive gap semiconductor and, in addition, it cannot explain the energy position of a quantized state in the charge accumulation layer which we have observed experimentally. Our data clearly show a state S 0 0.51 eV above the valence band maximum revealing no dispersion with variation of photon energy (or k Ќ ) but distinct dispersion with emission angle (or k k ) (see Figs. 1 and 2 of Ref. 2). Thus S 0 reveals two-dimensional character and may be assigned to a quantized state in the charge accumulation layer. The structure at 0.4 eV (which we have assigned to the conduction band minimum), in contrast, does show significant dispersion with variation of photon energy ͑k Ќ ͒ (it can be observed only in photoemission for photon energies around 12 eV) and thus cannot be quantized in the charge accumulation layer. The Comment is incorrect in assigning this state to a two-dimensional ground electric subband. In addition, the first excited subband (calculated by the authors of the Comment to lie at 0.625 eV) cannot be observed in the experimental spectra. Instead we ob-1536 0031-9007͞98͞81(7)͞1536(1)$15.00
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.