When quoting text or data from here, please state the reference as
D W Palmer, www.semiconductors.co.uk, 2005.01e (original date of this presentation of the data shown).
In this reply, these authors say that, because the results of calculations of the band
structure of InN depend on the theoretical model employed and on various InN properties
assumed in using the model, the arguments given in the Comment by Bechstedt et al 2004
(see below) based on their particular theoretical simulations cannot be considered to be
decisive. The reply presents the results of the authors' own simulations of absorption spectra
which do not produce a good fit to experimental data in the assumption of a bandgap of less
than 1 eV but give a much better fit if a bandgap value of 1.4 eV is assumed. They note that
the studies by both them and Bechstedt et al indicate that Mie resonances due to indium
precipitates produce peaks in the optical absorption spectrum.
Bechstedt et al 2004
Comment on the paper of Shubina et al 2004a (see below)
The authors of this paper argue that Shubina et al 2004a incorrectly concluded that the
observed sharp increase in the optical absorption near 1.4 eV is due to a direct band-gap of
that magnitude, and that, instead, that sharp increase arises from an effect of the
non-parabolicity of the InN band structure around the Gamma point upon the dielectric function
of the semiconductor. They say also that their own theoretical simulation of the optical
absorption of InN containing indium precipitates at a concentration of 2% indicates that the
observed absorption spectrum is consistent with a direct gap of less than 1 eV together with
absorption near 1 eV due to the indium inclusions.
Mahboob et al 2004
DFT-LDA Calculation whose Result is a Value of 0.58eV for the Energy Gap of Hexagonal InN
In conjunction with an experimental investigation of electron accumulation at clean (0001)
surfaces of wurtzite InN, this paper reported a theoretical study of the energy band structure
of that semiconductor using density-functional theory in the local density approximation.
When the pseudopotential used in the calculation was one that included self-interaction
corrections for the In 4d electrons, the calculated band structure indicated a direct
energy-gap value of 0.58 eV. It seems to the present reviewer, D W Palmer, that the authors
present that calculation as a more accurate version of the one reported by Davydov et al
in 2002 (see below) which gave an energy gap value of approximately 1.1 eV for wurtzite InN.
Shubina et al 2004a
Experimental Data that indicate an Energy Gap of close to 1.4eV for InN
This paper reported experimental data, obtained by photo-luminescence, cathodo-luminescence,
transmission electron microscopy and thermally detected optical absorption (TDOA) on MBE-grown
and MOCVD-grown hexagaonal InN, that the authors interpreted as indicating that the well known
PL emission from InN at about 0.7eV is due to a transition (a Mie resonance) at an electronic
state at the interface between metallic indium inclusions and the InN matrix, and that the
actual energy band-gap of hexagaonal InN, as determined from their TDOA data, is close to
1.4eV.
Arnaudov et al 2004
Near-Band-Edge Emission from InN Epitaxial Layers having Different Doping Levels
that indicate an Energy Gap of 0.69eV
From analysis of the shape and position of the near-band-edge photo-luminescence from InN
having different doping levels, the authors deduced the fundamental energy gap of InN as
0.692±0.002 eV for an electron effective mass of 0.042m0 at the cb minimum.
Butcher et al 2003
Consideration of the 0.7 PL Emission from InN
This paper proposed that the InN 0.7eV photo-luminescence, previously assigned corresponding to
the fundamental cb to vb energy gap, is due, instead, to an electronic transition in a deep
carrier trap having \ s> symmetry.
Matsuoka et al 2002
In(x)Ga(1-x)N at Room Temperature for x = 1.0, ie for InN
In experimental studies at room temperature on MOVPE-grown wurzite InN, Matsuoka et al,
2002, found strong photo-luminescence at 0.76 eV and definite optical absorption
at 0.7-1.0 eV; they deduced that the energy gap of wurzite InN is in the range
0.7-1.0 eV, that conclusion being consistent with the 0.7-0.8 eV value proposed by
Wu et al 2002 (see below).
Wu et al 2002
In(x)Ga(1-x)N at 77-300 K for x = 1.0, ie for InN
Using the measurement techniques of optical absorption, photo-luminescence and
photo-modulated reflectance applied to MBE-grown wurzite InN at 77K and 300K, Wu et al
2002 deduced an energy gap of 0.7-0.8eV for this semiconductor. That new
experimental result was unexpected and surprising since previous studies
(see below) had indicated an energy gap of 1.9-2.0 eV for wurzite-structure InN.
Davydov et al 2002
Evidence for a Narrow Fundamental Band Gap in Hexagonal InN
This paper presented data on the optical absorption and photo-luminescence of hexagonal InN
that, for the first time, showed a direct energy gap of approximately 0.9 eV, ie much lower
than the values reported previously in other work. The paper reported also a calculation
using density-functional theory in the local density approximation in which a self-interaction
correction was used for the In 4d electrons; this work suggested a theoretical direct energy gap
of about 1.1eV, which the paper stated should be considered as being in reasonable agreement
with the reported measured value.
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