@MastersThesis{Okazaki:2015:EsFiFi,
author = "Okazaki, Anderson Kenji",
title = "Estudo de filmes finos de PbTe:CaF2 crescidos por epitaxia de
feixe molecular",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2015",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2015-02-25",
keywords = "telureto de chumbo, fluoreto de c{\'a}lcio, epitaxia por feixe
molecular, lead telluride, calcium fluoride, molecular beam
epitaxy.",
abstract = "Este trabalho tem como objetivo investigar as propriedades
estruturais e el{\'e}tricas de filmes de PbTe dopados com
CaF\$_{2}\$. Com esse prop{\'o}sito, filmes de
PbTe:CaF\$_{2}\$ foram crescidos pela t{\'e}cnica de epitaxia
de feixe molecular sobre substrato cristalino de BaF\$_{2}\$
(111), com a temperatura da fonte de CaF\$_{2}\$ variando entre
500\$^{º}\$C e 1250\$^{º}\$C. A espessura dos filmes crescidos
variou de 1,8 a 3,5 \$\mu\$m, e filmes com espessura acima de
2,4 \$\mu\$m apresentaram uma diminui{\c{c}}{\~a}o na
densidade de defeitos em sua superf{\'{\i}}cie. Nas amostras com
oferta de CaF\$_{2}\$. abaixo de 1010\$^{º}\$C, as imagens de
difra{\c{c}}{\~a}o de el{\'e}trons de alta energia medidas
\emph{in situ} exibiram um padr{\~a}o caracter{\'{\i}}stico de
uma superf{\'{\i}}cie plana com degraus. Para temperaturas
maiores da fonte de CaF\$_{2}\$., os padr{\~o}es revelaram que
a deposi{\c{c}}{\~a}o ocorreu em ilhas. A presen{\c{c}}a de
pequenos aglomerados observados nas imagens de microscopia de
for{\c{c}}a at{\^o}mica corrobora com este resultado. Uma
n{\'{\i}}tida fase de condensados de CaF\$_{2}\$. foi
observada nas varreduras \$\omega\$-2\$\Theta\$ das
an{\'a}lises de difra{\c{c}}{\~a}o de raios-x para as amostras
que continham estas ilhas. Nas amostras com oferta de dopante
abaixo de 900\$^{º}\$C, os valores da largura {\`a} meia altura
do pico de Bragg (222) do PbTe ficaram pr{\'o}ximos a
103\${{"}}\$, valor similar ao da amostra de refer{\^e}ncia sem
dopante, mostrando que a presen{\c{c}}a do fluoreto n{\~a}o
afetou significativamente a qualidade cristalina dos filmes. O
par{\^a}metro de rede manteve-se muito pr{\'o}ximo ao valor
tabelado do PbTe volum{\'e}trico (6,462 A), revelando que a
oferta de CaF\$_{2}\$., n{\~a}o causou uma tens{\~a}o
significativa nos filmes. A energia de gap {\`a} temperatura
ambiente tamb{\'e}m se manteve pr{\'o}xima ao valor tabelado
para o PbTe (0,32 eV), mostrando que a adi{\c{c}}{\~a}o do
dopante n{\~a}o causou a forma{\c{c}}{\~a}o de uma nova liga. A
concentra{\c{c}}{\~a}o de portadores dos filmes de
PbTe:CaF\$_{2}\$. flutuou entre 1,5 10\$^{17}\$ e 3,6
10\$^{17}\$ cm\$^{-3}\$ a 77 K, n{\~a}o exibindo um
comportamento sistem{\'a}tico {\`a} medida que a oferta do
fluoreto aumentava. Os resultados das medidas el{\'e}tricas
mostraram que a oferta de CaF\$_{2}\$. durante o crescimento
n{\~a}o produziu um efeito de dopagem extr{\'{\i}}nseca para o
PbTe. ABSTRACT: This work aims to investigate the structural and
electrical properties of PbTe films doped with CaF\$_{2}\$. For
this purpose, PbTe:CaF\$_{2}\$. films were grown by molecular
beam epitaxy on (111) BaF\$_{2}\$. crystalline substrates, with
the CaF\$_{2}\$. source temperature varying between
500\$^{º}\$C and 1250\$^{º}\$C. The thickness of the grown
films ranged from 1.8 to 3.5 \$\mu\$m and films thicker than
2.4 \$\mu\$m presented a lower surface defect density. For
samples grown with a CaF\$_{2}\$. source temperature lower than
1010\$^{º}\$C, the high energy electron diffraction images
measured \emph{in situ} exhibited a pattern characteristic of a
flat surface with steps. For higher CaF2 source temperature, the
patterns revealed that the deposition occurred in islands. The
presence of small agglomerates observed in the atomic force
microscopy images corroborates with this result. An evident phase
of CaF\$_{2}\$. condensates in the samples that presented these
islands was observed in the \$\mu\$-2\$\theta\$ scans of the
x-ray diffraction analysis. For the samples with a dopant offer
lower than 900\$^{º}\$C, the values of the full width at half
maximum of the (222) PbTe Bragg peak stayed near to
103\${{"}}\$, a value similar to the one of the undoped
reference sample, what demonstrates that the presence of the
fluoride did not affect significantly the crystalline quality of
the PbTe films. The lattice parameter of the grown films remained
very close to the tabulated value of the bulk PbTe (6.462 A),
revealing that the CaF\$_{2}\$. offer did not cause a
significant stress in the films. The energy gap at room
temperature also remained close to the tabulated value of PbTe
(0.32 eV), showing that the CaF\$_{2}\$. addition did not form a
new alloy. The carrier concentration of the PbTe:CaF2 films
fluctuated between 1.5 10\$^{17}\$and 3.6 10\$^{17}\$
cm\$^{-3}\$ at 77 K, and did not exhibit a systematic behavior
as the fluoride offer raised. The electrical measurement results
showed that the CaF\$_{2}\$. offer during growth did not produce
an extrinsic doping effect on PbTe.",
committee = "Rappl, Paulo Henrique de Oliveira (presidente/orientador) and
Abramof, Eduardo (orientador) and An, Chen Ying and Peres,
Marcelos Lima",
copyholder = "SID/SCD",
englishtitle = "Study of PbTe:CaF2 thin films grown by molecular beam epitaxy",
language = "pt",
pages = "124",
ibi = "8JMKD3MGP3W34P/3HU459L",
url = "http://urlib.net/ibi/8JMKD3MGP3W34P/3HU459L",
targetfile = "publicacao.pdf",
urlaccessdate = "27 abr. 2024"
}