Proceedings Article | 17 October 2012
Kelly Rickey, Qiong Nian, Genqiang Zhang, Liangliang Chen, S. Venkataprasad Bhat, Yue Wu, Gary Cheng, Xiulin Ruan
KEYWORDS: Thermal effects, Annealing, Glasses, Photovoltaics, Scanning electron microscopy, Quantum dots, Crystals, Particles, Thin films, Nanowires
Effects of rapid thermal annealing (RTA) and dual compression-pulse-laser sintering (compression-PLS) on
photovoltaic, CdTe nanowire (NW) and quantum dot (QD) films are investigated. Unlike regular furnace annealing,
RTA involves raising the temperature of a substrate’s atmosphere by several hundred degrees in a matter of seconds,
letting it sit for 30 to 120 seconds, then cooling it back to T0. To the best of our knowledge, such treatments of CdTe
nanocrystal (NC) films have not been documented. In compression-PLS, a large pressure (MPa) is applied to a film
through a laser-pulsing mechanism. Next, a high-energy, high frequency laser beam is pulsed onto it for sintering.
During the compression, we used a single pulse of 5 nanoseconds. For the sintering, we used a 7.05 mJ beam for two
pulses, at 25 ns per pulse. Such parameters were determined from SEM and other preliminary film characterization
results. Morphology, material content, and conductivity of the films are analyzed before and after treatment using
tunneling and scanning electron microscopy, EDS, and two-probe measurements, respectively.
This study provides new knowledge regarding the morphological and structural outcomes of RTA and
compression-PLS on CdTe nanoparticle films. Furthermore, RTA and compression-PLS can increase the film electrical
conductivity by improving their contact with each other. We found that RTA partially sinters the film and enhances inplane
current density by a factor of ~1.7, for a values on the order of ~10-7A/cm2. Compression-PLS successfully sinters
the NW film and improves current density up to a factor of ~167, for values on the order of ~10-5 A/cm2. On the other
hand, QD films do not exhibit current density improvement with treatments. These values remain on the order of ~10-7
A/cm2.
The resistivities of the sintered NW films reach as low as 6.7*106 Ω*cm, while the RTA’d NW film has a
resistivity on the order of 108 Ω*cm. These values are comparable to values of bulk and thin-film CdTe: single
crystalline, undoped CdTe resistivity values range from 105 to 108 Ω*cm,8,9 while polycrystalline thin-film values range
from 104 to 106 Ω*cm.11,12 The QD films also have comparable resistivities to these results, albeit on the higher side.
