HgSe: Metal or Semiconductor?

Abstract

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...

Quasiparticle band structures ofβ-HgS, HgSe, and HgTe

“…Photoelectron spectroscopic experiments carried out by Gawlik et al 4 on n-type HgSe indicated that this material should have a positive band gap of 0.42 eV. Later experiments, including the photoemission study by Janowitz et al 5 could not verify this, and it was concluded that HgSe is a semimetal.…”

Electronic structure of some mercury chalcogenides using Compton spectroscopy

“…An exclusive group with these properties is known as semimetal or zero-gap semiconductors group (Delin and Kluner, 2002). Due to peculiar properties of mercury chalcogenides, many theoretical and experimental investigations have been undertaken which mainly include electronic-structure calculations (Rohlfing and Louie, 1998;Orlowski et al, 2000;Delin and Kluner, 2002;Delin, 2002;Fleszar and Hanke, 2005;Moon and Wei, 2006), photoemission spectroscopy (Gawlik et al, 1997), magneto-optical Fourier transform spectroscopy (von TruchseX et al, 2000), some optical properties (Markowski and Podgorny, 1992), etc.…”

First principles investigations of HgX (X=S, Se and Te)

“…HgS in the structure of zinc-blende (ZB) is used to produce nanocrystals or thin films [2]. Topological insulators, optoelectronic and spintronic applications, photovoltaic/photoconductive devices IR detectors and emitters, ohmic contact and removing mercury from exhaust gases, are some examples of their technological applications of mercury chalcogenides [3][4][5][6][7].…”