Silicon-germanium films deposited by low-frequency plasma-enhanced chemical vapor deposition: Effect of H₂ and Ar dilution

Abstract

We have studied structure and electrical properties of Si1−YGeY:H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y = 0 to Y = 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H2. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y = 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity γ-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.

Study of Si and Ge Atoms Termination Using H-Dilution in SiGe:H Alloys Deposited by Radio Frequency (13.56 MHz) Plasma Discharge at Low Temperature

“…Vd(RH) shows a reduction from Vd = 1.2 to 0.5 A/s with a change in RH from RH = 9 to 40 and only a small change (practically negligible) in the range RH = 40 to 80. Comparing these Vd values with those reported in reference [9] for SiGe:H films deposited by low frequency (LF) PECVD and high temperature we noticed similar Vd values for low Ge content (about 0.1 in the gas phase) to those for RF PECVD films. On the other hand, values of the deposition rate of Vd = 0.9 ± 0.1 Å /s are found in reference [18] for film growth with 0.5 Ge content in the gas phase.…”

“…One promising technique to improve the film quality of Si X Ge Y :H Z alloys deposited by PECVD is the hydrogen dilution method [8,9]. Many groups have reported results obtained by this technique and…”

Effect of Hydrogen Dilution on Structure and Electronic Properties of Ge:H and GeYSi1-Y Films Deposited by Low Frequency Plasma

“…This data suggests Ge preferential incorporation with an incorporation factor Y Ge =1.92-1.94 [12]. For Ge:H films a trend of decreasing V d with R with a local maxima at R=50 is shown, and for Ge Y Si 1-Y :H films V d grows with R from R=20 to 40, and shows practically no change in the range of R=40 to 60 and then decreases.…”

“…Earlier works can be found in several reviews [8,9]. [11,12]. However, deposition conditions that provide higher ion bombardment during film growth are considered to be favorable for deposition of good quality Ge Y Si 1-Y :H and Ge:H films [10].…”

Nano-structured GeySi1-y:H Films Deposited by Low Frequency Plasma for Photovoltaic Application

“…Our previous study [10][11][12] has revealed a significant effect of hydrogen dilution R H on microstructures, hydrogen incorporation and electronic properties. It was observed that optimization of deposition conditions and especially of R H could result in rather well organized microstructure with narrow distribution function of nano-grains over heights and diameters (i.e.…”