Ultra-highly doped Si{sub 1-x}Ge{sub x}(001):B gas-source molecular-beam epitaxy: Boron surface segregation and its effect on film growth kinetics
Si{sub 1-x}Ge{sub x}(001) layers doped with B concentrations C{sub B} between 2x10{sup 16} and 2x10{sup 21}cm{sup -3} were grown on Si(001)2x1 at T{sub s}=500--700{sup o}C by gas-source molecular-beam epitaxy (GS-MBE) from Si{sub 2}H{sub 6}, Ge{sub 2}H{sub 6}, and B{sub 2}H{sub 6}. Secondary-ion mass spectrometry measurements of modulation-doped structures demonstrate that B doping has no effect on the Ge incorporation probability. Steady-state B and Ge surface coverages ({theta}{sub B} and {theta}{sub Ge}) were determined as a function of C{sub B} using in situ isotopically tagged temperature-programmed desorption. Results for Si{sub 0.82}Ge{sub 0.18} layers grown at T{sub s}=500{sup o}C show that {theta}{sub Ge} remains constant at 0.63 ML while the bulk B concentration increases linearly up to 4.6x10{sup 20}cm{sup -3}, corresponding to saturation coverage at {theta}{sub B,sat}=0.5ML, with the incident precursor flux ratio {xi}=J{sub B{sub 2}H{sub 6}}/(J{sub Si{sub 2}H{sub 6}}+J{sub Ge{sub 2}H{sub 6}}). B is incorporated into substitutional electrically active sites over this entire concentration range. At higher B concentrations, C{sub B} increases faster than {xi} and there is a large decrease in the activated fraction of incorporated B. The B segregation enthalpy during Si{sub 0.82}Ge{sub 0.18}(001) growth is -0.42 eV, compared to -0.53 and -0.64 eV during Si(001):B and Ge(001):B GS-MBE, respectively. Measured segregation ratios r{sub B}={theta}{sub B}/x{sub B}, where x{sub B} is the bulk B fraction, range from 15 to 500 with a temperature dependence which is consistent with equilibrium segregation. Film deposition rates R{sub SiGe}(C{sub B}) decrease by up to a factor of 2 with increasing C{sub B}{>=}5x10{sup 19}cm{sup -3}, due primarily to a B-segregation-induced decrease in the dangling bond density. The above results were used to develop a robust model for predicting the steady-state H coverage {theta}{sub H}, {theta}{sub B}, {theta}{sub Ge}, and R{sub SiGe} as a function of {xi} and T{sub s}.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40204901
- Journal Information:
- Journal of Applied Physics, Vol. 89, Issue 1; Other Information: DOI: 10.1063/1.1330244; Othernumber: JAPIAU000089000001000194000001; 005102JAP; PBD: 1 Jan 2001; ISSN 0021-8979
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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