Study of substrate diffusion in epitaxial n-type CdSe films grown on GaAs (001) by pulsed laser ablation Page: 3 of 9
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
STUDY OF SUBSTRATE DIFFUSION IN EPITAXIAL N-TYPE CdSe FILMS
GROWN ON GaAs (001) BY PULSED LASER ABLATION
JAEWON PARK, CHRISTOPHER M. ROULEAU, AND DOUGLAS H. LOWNDES
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6056
ABSTRACT
N-type CdSe films with thicknesses of 470-630 nm were grown on (001) and 2*-miscut GaAs
wafers by ArF (193 nm) pulsed laser ablation of stoichiometric CdSe targets at platen temperatures
(Tp) of 250-425*C in vacuum and ambient Ar gas. Film-substrate interdiffusion was studied with
Auger depth profiling, as well as energy dispersive x-ray fluorescent spectroscopy (EDS). Both
techniques showed that extensive interdiffusion took place at the film-substrate interface for CdSe
films grown at Tp> 355*C but was greatly reduced at Tp=250*C. Tilting the substrate to be
approximately parallel to the ablation plume as well as decreasing the ambient gas pressure also
reduced film-substrate interdiffusion.
INTRODUCTION
CdSe with a band gap of 1.7 eV (kg=729 nm) and a free exciton binding energy of 14 meV [1]
at room temperature has potential for opto-electronic devices operating in the red to near IR spectral
range. N-type cubic CdSe also is of interest for heterostructures with p-ZnTe since these two
compounds have a lattice constant mismatch of less than 1% (aznTe=6.1A, acdSe=6.052 A).
However, CdSe or other compound semiconductor films for such applications must satisfy a
number of requirements, including (i) epitaxial growth; (ii) high dopability; (iii) near-ideal film
stoichiometry; and (iv) freedom from contaminants except for dopants.
Epitaxial CdSe films have been grown on GaAs (001) and on ZnSe/GaAs(001) by molecular
beam epitaxy (MBE) [2,3] and metalorganic MBE [4]. Recently, films of epitaxial CdSe, as well
as other compound semiconductors [5], were also grown on (001) GaAs by pulsed laser
deposition (PLD) [6]. Despite these demonstrations of epitaxial growth, the optimum growth
conditions to obtain high quality films require more study, primarily because of the large (7.1%)
lattice mismatch between GaAs ( a = 5.653A) and CdSe.
Impurities can be introduced into a film from the deposition chamber atmosphere as well as by
substrate diffusion during film growth. Although environmental impurities are reasonably
controllable when a low-pressure gas is used for dopants incorporation during PLD [5,7], the
diffusion of substrate atoms into the film often takes place in the temperature range used for
epitaxial growth, regardless of the growth technique [8,9]. Film-substrate interdiffusion is difficult
to control in many cases, especially for lattice-mismatched heteroepitaxial systems, and becomes
more important as the thickness of the layers in semiconductor quantum structures decreases. For
instance, interdiffusion can affect the electron and phonon states at the interface and may change
the electrical and optical properties of compound semiconductor epilayers. Film stoichiometry is
crucial to control the electronic properties of films used in devices since a point defect (vacancy,
interstitial) concentration of only 1 part in 104 can prevent electrical activation of dopants [5].
This paper deals with film-substrate interdiffusion for epitaxial CdSe films deposited onto
GaAs (001) by PLD. The studies were conducted with Auger electron spectroscopy (AES) and
energy dispersive x-ray spectroscopy (EDS).
EXPERIMENTAL PROCEDURES
The film deposition set-up is schematically described in Fig. 1. An ArF (3-5 Hz, 193 nm)
excimer laser was used for PLD of CdSe films in an ultra high vacuum (UHV) chamber (base
pressure < 10-9 torr). 6N purity Ar gas was introduced into the chamber through a mass-flow
control manifold and the ambient gas pressure was controlled from zero to 50 mtorr using a
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Park, J.; Rouleau, C.M. & Lowndes, D.H. Study of substrate diffusion in epitaxial n-type CdSe films grown on GaAs (001) by pulsed laser ablation, report, April 1, 1998; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc709676/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.