|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||O4, Comparative Studies of Carrier Dynamics in 3C-SiC Layers Grown on Si and 4H-SiC Substrates
||jawad ul hassan, Patrik Scajev, Kestutis Jarasiunas, Masashi Kato, Anne Henry, Peder Bergman
|On-Site Speaker (Planned)
||jawad ul hassan
Large lattice mismatch and different thermal expansion coefficient leads to high structural defect density in 3C-SiC layers grown on Si substrates (3C/Si). These extended defects severely deteriorate optical and electrical properties of the crystal. Heteroepitaxial growth of 3C on hexagonal 4H-SiC substrates (3C/SiC) could be beneficial to avoid growth induced extended defects and hence may result in superior crystalline quality. We performed comparative studies of optical properties and carrier dynamics in 3C-SiC layers grown on Si and SiC substrates using three optical techniques. 3C-SiC n-type layers (nitrogen doping ~ 1x10<SUP>17 </SUP>cm<SUP>-3</SUP> and thickness of ~ 300 Ám) were grown on undullant Si substrates and free standing 3C layers were obtained after mechanically polishing away Si substrate. Low doped n-type layers (nitrogen doping ~ 1 x 10<SUP>15</SUP> cm<SUP>-3</SUP> and thickness of ~ 100 Ám) were grown on nominally on-axis 4H-SiC substrates using horizontal hot-wall chemical vapor deposition reactor in Link÷ping university. Important electronic parameters for 3C-SiC, such as carrier lifetime, diffusion coefficient and diffusion length were determined using different optical techniques. These included light diffraction on transient free carrier grating (TG), free carrier absorption (FCA) and time-resolved photoluminescence (TRPL). The measurements were made over a wide range of excess carrier densities, ΔN = 10<SUP>16</SUP> - 10<SUP>19</SUP> cm<SUP>-3</SUP>, and temperatures, T = 80 - 800 K. The carriers were excited by a frequency tripled Nd:YLF-laser at 351 nm. Low temperature photoluminescence spectroscopy was also performed to observe the purity of the material. PL spectra at 5 K revealed similar features in both layers over wide energy range. The near band edge emission was dominated by nitrogen-bound exciton recombinations while very weak DAP transitions were observed at lower energies. In contrary, FCA decay kinetics provided very different carrier lifetimes of 16 ns in (3C/Si) layers and 100 ns in (3C/SiC) layers at room temperature, thus indicating higher structural quality of on-axis grown 3C/SiC layers. We note a long lifetime of ~130 ns at the backside of free standing 3C/Si layers (nearby 3C/Si interface). A higher density of SFs has been reported in this region; however, the origin of so long lifetime in high SF density region is not known. In the 3C/SiC layers, the temperature dependence of carrier lifetime in 80-800 K range revealed non-monotonous increase of lifetime from ~50 ns to ~300 ns. The TG decay times in both layers revealed similar D(T) dependences in 80-800K range, with bipolar mobility values of 140-160 cm<SUP>2</SUP>/Vs at RT. The mobility and lifetime data in 3C/SiC layers provided carrier bipolar diffusion length of ~6.5 Ám and hole diffusion length of ~4.5 Ám, being the largest values reported up to now for 3C.