Synthesis, structural, optical, and electrical properties of continuous wave and pulse laser sintered semiconductor Ge films

Abstract

The crystallization process of Ge films by a continuous wave (CW) and a pulsed laser is very effective for producing smooth, homogeneous, and crack-free polycrystalline films to use in transistors, photodetectors, and photovoltaic applications. However, little progress has been made to directly crystallize Ge films based on micro/nanoparticles (NPs) using the laser sintering (LS) process. In this paper, a simultaneous LS and crystallization process of Ge micro/nanoparticles to develop thick polycrystalline films on silicon substrates is demonstrated. Silicon substrates with a SiO2 insulating layer on top were considered for compatibility with complementary metal-oxide-semiconductor (CMOS) technology. The LS process was applied to solution deposited micro/nanoparticles, 5 µm thick Ge films using both CW mode (infrared (IR) laser of wavelength 1070 nm) and pulse mode (UV laser of wavelength 355 nm) laser. After the LS process, around 2-2.5 µm thick film of polycrystalline Ge (pc-Ge) was achieved with optical and electrical properties comparable to traditionally developed chemical vapor deposited films. The crystallinity of the pc-Ge films was evaluated by Raman spectroscopy and XRD diffraction. The laser-sintered films exhibited a Raman peak at 300 cm−1 and XRD 2θ peak at 27.35, which indicated the poly-crystalline structure. The fabricated film showed high hole mobility of 203 cm2/V.s, without any doping and film electrical resistivity value of 6.24x105 Ω-cm. The developed LS process allows the quick deposition of polycrystalline thick films, removing surface porosity and voids, increasing films adhesion with the substrate, and faster thermal annealing.