Resonant photoemission study on the boron 1sexciton of the wide-band-gap semiconductorc-BN

Abstract

The B 1s exciton spectrum of the wide-band-gap semiconductor c-BN has been studied by resonant photoemission spectroscopy. The core-exciton band is found with a binding energy of about 1.2 eV. The constant-initial-state spectra for the valence-band features indicate that the B 1s exciton is the intermediate state for the resonant photoemission from the valence band. A satellite is found below the lower valence band by the resonant photoemission at B 1s exciton. The energy distribution curves of the valence band are qualitatively in agreement with the energy-band density-of-states curves but the discrepancy is conspicuous for the conduction band. The remarkable Fermi-level shift is found between p-type and n-type c-BN in accord with the rigid-band model, in spite of the large band-bending e8'ect.

Resonant soft-x-ray emission study in relation to the band structure of cBN

“…However, the band calculations, which were carried out by means of local density approximation ͑LDA͒ and other methods, indicate smaller band gaps. [27][28][29][30][31][32][33][34][35][36] On the other hand, a quasiparticle band calculation is in good agreement with our result. The cBN band gap and valence bandwidths obtained by the present study are listed in Table I.…”

“…The core exciton has been already observed by Fomichev et al 9 in TPY and by Shin et al in the total electron yield ͑TEY͒ spectra. 33 Shin et al measured the resonant PES and CIS ͑constant initial state͒ spectra around CE region, and found the strong resonance enhancement of the valence band structure at the CE structure. This fact also suggests that the CE is a core exciton structure.…”

“…Since cBN has several interesting physical properties, such as a wide band gap, extreme hardness, and a high melting point, the electronic structure of cBN has been studied by optical reflectivity, absorption, x-ray emission spectroscopy, [9][10][11][12][13][14][15] and photoemission spectroscopy. 33 Many theoretical band calculations have been carried out, [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] because of its simple crystal structure and small number of electrons. However, the correspondence between the theoretical calculation and the experiment has not been so good.…”

Raman vs Rayleigh scattering in the soft-x-ray region

“…These numerical values, with the exception of W, are estimated from experimental data. 8,9 The value of W is only an adjustable parameter and this choice will be discussed later. The values of V 0 and ⌫ c we adopted are consistent with the very small reflectance of the order of 10 Ϫ5 -10 Ϫ6 near the core-exciton resonance.…”

“…Carson and Schnatterly 7 found that both the exciton intensity and binding energy could be explained with a Wannier model. Recently, synchrotron radiation sources and measurement systems have been improved to the extent that Raman scattering spectra in the soft-x-ray region, 8 and the core-exciton structure in total photon yield ͑TPY͒ spectra, 9 have been observed. These are usually interpreted by conventional extensions of concepts established in the visible frequency region.…”