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Homoepitaxy of ZnTe on (100) oriented substrates: Technology issues and MOVPE growth aspects
Author(s) -
Traversa M.,
Lovergine N.,
Prete P.,
Tapfer L.,
Mancini A. M.
Publication year - 2005
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.200410476
Subject(s) - hillock , nucleation , materials science , metalorganic vapour phase epitaxy , substrate (aquarium) , stoichiometry , wafer , epitaxy , layer (electronics) , crystallography , cathodoluminescence , luminescence , optoelectronics , nanotechnology , chemistry , composite material , oceanography , organic chemistry , geology
The metalorganic vapour phase epitaxy of ZnTe on single crystal (100)ZnTe:P wafers is reported. The technological steps to prepare a substrate surface suitable for the high quality homoepitaxy of ZnTe are identified and optimised in terms of structural and morphological properties of overgrown epilayers. Removal of ∼7 µm of material from the ZnTe:P wafers by chemical etching in 1% Br 2 ‐methanol solution proved necessary to achieve a sufficiently smooth and homogeneous surface; in‐situ H 2 heat treatment of the wafers at 350°C immediately before growth ensures optimal desorption of residual oxides, allowing epilayer crystalline quality comparable to the substrate. However, the structure of epilayers degrades for growth temperatures (T G ) above 350 °C due to the occurrence of stacking faults (SFs) within ∼200‐300 nm from the epilayer‐substrate interface. Accordingly, the epilayer band‐edge luminescence vanishes below 350 nm, indicating a worsening of the material radiative efficiency in very thin epilayers. The epilayer surface morphology is the result of a complex interplay between SF nucleation and Te:Zn ad‐atom stoichiometry during growth. Almost featureless morphologies are obtained for growth at 350 °C, i.e. under nearly stoichiometric surface conditions. Pyramid‐like hillocks develop instead for T G ≥ 360 °C, corresponding to Te‐rich surface conditions, their density rapidly increasing up to around 9 × 10 6 cm –2 at T G = 400 °C. Hillocks occur in close pairs on the epilayer surface, their nucleation being strongly reduced if a thin ZnTe buffer layer is grown at low (325 °C) temperature, i.e. if SFs do not occur at the epilayer‐substrate interface. This demonstrates that hillocks form as a result of three‐dimensional growth around partial dislocations pairs bounding SFs, the phenomenon being driven by Te ad‐atoms experiencing a Schwoebel potential barrier at the surface step edges around the dislocations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)