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Contactless electroreflectance studies of surface potential barrier in AlGaN/n‐AlGaN structures with various Al concentrations
Author(s) -
Janicki Ł.,
Kudrawiec R.,
Pakuła K.,
Stępniewski R.,
Misiewicz J.
Publication year - 2015
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201451598
Subject(s) - barrier layer , electric field , materials science , oscillation (cell signaling) , rectangular potential barrier , layer (electronics) , surface states , optoelectronics , fermi level , surface layer , wide bandgap semiconductor , analytical chemistry (journal) , condensed matter physics , surface (topology) , chemistry , nanotechnology , physics , electron , biochemistry , geometry , mathematics , quantum mechanics , chromatography
Contactless electroreflectance spectroscopy has been applied to study the surface potential barrier in Al x Ga 1− x N/n‐Al x Ga 1− x N structures with 0 ≤ x ≤ 0.25 grown by metaloorganic vapor phase epitaxy. A strong band‐to‐band transition followed by Franz–Keldysh oscillation (FKO) was clearly observed for all samples. The value of built‐in electric field was determined from the period of FKO, and the surface potential barrier was calculated with knowledge of the thickness of undoped Al x Ga 1− x N layer. For a set of GaN/n‐GaN structures with different thickness of undoped GaN layer (30–120 nm) an analysis of built‐in electric field gives the surface potential barrier of 0.59 ± 0.03 eV. For Al x Ga 1− x N(60 nm)/n‐Al x Ga 1− x N structures with 0.09 ≤ x ≤ 0.25 the surface potential barrier does not vary with Al concentration within the experimental accuracy. In this case the position of the Fermi level at the surface has been estimated to be ∼1.4 eV. The increase of surface potential barrier from 0.59 eV for GaN to 1.4 eV for AlGaN with 0.09 ≤ x ≤ 0.25 is attributed to low concentration of n‐type non‐intentional residual dopants in the undoped Al x Ga 1− x N layer as well as the presence of Al atoms at the surface and their higher sensitivity to oxidation and/or creation of defects states which are not present at GaN surfaces.