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

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/NPs 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/NPs, 5 mu m thick Ge films using both CW mode (infrared laser of wavelength 1070 nm) and pulse mode (UV laser of wavelength 355 nm) laser. After the LS process, around 2-2.5 mu m 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 x-ray diffraction (XRD). The laser-sintered films exhibited a Raman peak at 300 cm(-1) and XRD 2 theta peak at 27.35, which indicated the poly-crystalline structure. The fabricated film showed high hole mobility of 203 cm(2) V-1 s(-1), without any doping and film electrical resistivity value of 6.24 x 10(5) omega-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.