Abstract
As an indirect band gap material, Germanium (Ge) has low efficiency of radiative recombination in the wavelength area of about 1550 nm. However, the difference between the direct and indirect band gap is very small (～140 meV) and photoluminescence emission ability of Ge could be greatly enhanced by heavy n-doping process. In this work, Ge growth directly on Si (001) substrate by molecular beam epitaxial (MBE) technique and a high n-doping level in Ge was obtained owning to using GaP decomposition source. The GaP solid source produces P2 molecules instead of P4 molecules, which have higher sticking coefficient than that of P4 comparing to the traditional doping method from PH3 gas precursor molecules. The dependence of optical property on Ge film thickness is also studied. The out-diffusion phenomenon of phosphorus dopant has been observed through SIMS profile analysis. An activated phosphorus concentration can be achieved up to more than 2 × 1019 atoms?cm&minus3 confirmed by Hall effect measurement. This result contributes to realization of Ge-on-Si devices for optoelectronic applications.
Highlights
In the last few years, research on the tensile strained and n-doped Ge thin film on Si substrate has been the subject of many investigations with the hope to realize an Ge active layer in optoelectronic devices totally compatible with CMOS technology [1] [2] [3] [4] [5]
As can be seen from the figure, the photoluminescence intensity increases with increasing the temperature of the GaP source from 600 ̊C to 725 ̊C and the highest PL intensity is obtained at 725 ̊C
We investigate the effect of film thickness on the optical properties of P doped Ge layers
Summary
In the last few years, research on the tensile strained and n-doped Ge thin film on Si substrate has been the subject of many investigations with the hope to realize an Ge active layer in optoelectronic devices totally compatible with CMOS technology [1] [2] [3] [4] [5]. It has been shown that Ge could become direct band gap material when applying a tensile strained value of 1.9% on Ge layer [6]. Normally method for n-doped Ge film from phosphorus is by mean of using PH3 gas, which produces tetrahedral phosphorus molecule with low sticking coefficient and the highest doping concentration only obtained in the range of 1018 - 1 × 1019 atoms∙cm−3. In this work we implement n-doped process by using GaP specific decomposition solid source, which produce P2 molecule with sticking coefficient 10 times higher than that of P4 [9] [10]. It is shown that activated electron concentration up to 2 × 1019 atoms∙cm−3 can be obtained confirming by both Hall effect measurement and band gap narrowing phenomenon
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