The properties of CdO films formed by low-pressure chemical vapor depositio
n were investigated as a function of deposition temperatures from 150-450 d
egreesC. Atomic force microscopy, X-ray diffraction, and transmission elect
ron microscopy revealed that the grain size, bulk crystallinity, and intrag
rain quality all improved with increasing temperature. Spectrophotometry sh
owed that the optical bandgap decreased from 3.10 to 2.35 eV with increasin
g deposition temperature, whereas Hall measurements indicated that carrier
concentration decreased from mid 10(20) to low 10(19) cm(-3). Over the same
range of temperature, the mobility increased from similar to6 to 216 cm(2)
V-1 s(-1), the latter being the highest value ever achieved for CdO in any
form. The high mobility achieved at increased deposition temperature was d
ue partly to a reduction in the effective mass of carriers but mainly to an
increase in their relaxation time associated with improved crystallinity.
The optical and Hall measurements suggest that the higher optical bandgap f
or low deposition temperature is likely due to a Moss-Burstein shift, from
which the reduced effective mass was estimated as approximately 0.11 m(e).
A novel charge-transport method was used to determine the density-of-states
effective mass of electrons. This mass increased from 0.14-0.18 m(e) with
carrier concentration. Using this range of values and the reduced effective
mass, we calculated that the approximate value of the density-of-states va
lence-band effective mass is 0.28-0.51 m(e). (C) 2001 The Electrochemical S
ociety.