Phosphorus incorporation during Si(001):P gas-source molecular beam epitaxy: Effects on growth kinetics and surface morphology

Abstract

The effects of P doping on growth kinetics and surface morphological evolution during Si͑001͒:P gas-source molecular beam epitaxy from Si 2 H 6 and PH 3 at temperatures T s = 500-900°C have been investigated. With increasing PH 3 / Si 2 H 6 flux ratio J P/Si at constant T s , we observe a decrease in the film growth rate R and an increase in the incorporated P concentration C P , both of which tend toward saturation at high flux ratios, which is accompanied by increased surface roughening and pit formation. At constant J P/Si , R increases with increasing T s , while C P initially increases, reaches a maximum at T s = 700°C, and then decreases at higher growth temperatures. We use in situ isotopically tagged D 2 temperature programed desorption ͑TPD͒ to follow changes in film surface composition and dangling bond density db as a function of J P/Si and T s. Measurements are carried out on both as-deposited Si͑001͒:P layers and P-adsorbed Si͑001͒ surfaces revealing ␤ 1 and ␤ 2 peaks due to D 2 desorption from Si monohydride and dihydride species, respectively, as well as the formation of a third peak ␤ 3 corresponding to D 2 desorption from mixed Siu P dimers. Dissociative PH 3 adsorption on Si͑001͒ results in a decrease in db and an initial increase in P surface coverage P with increasing T s. Saturation P values reach a maximum of ϳ1 ML at T s = 550°C, and decrease with T s Ͼ 600°C due to the onset of P 2 desorption. Comparison of P ͑T s ͒ results obtained during film growth with postdeposition C P ͑T s ͒ results reveals the presence of strong P surface segregation. From measurements of P versus C P in Si͑001͒:P layers grown as a function of T s , we obtain a P segregation enthalpy ⌬H s = −0.86 eV. By using the combined set of results, we develop a predictive model for C P versus T s and, J P/Si incorporating the dependence of the PH 3 reactive sticking probability S PH 3 on P , which provides an excellent fit to the experimental data.

Laterally assembled nanowires for ultrathin broadband solar absorbers

“…A NW array supports no additional coupled mode because of the low quality factor of a single NW cavity. Therefore, if the light absorption in a single NW is appropriately tuned by tailoring the NW's morphology or composition [8,[14][15][16][17][18], a NW array composed of these single NWs will possess the same absorption features as that of a single NW. This demonstrates the importance of optical design at the single-NW level.…”

“…Nanowires (NWs) are well-suited for a variety of optoelectronic applications [1][2][3][4][5][6][7][8][9][10][11][12][13] in part because their morphology [8,14,15] and composition [16][17][18] can be finely tuned during synthesis rather than post hoc as in top-down fabrication. In addition, NWs can have diameters less than the wavelength of light, allowing for large scattering to physical cross section [19,20] and localized optical resonances [7,8].…”

Semiconductor nanowires: a platform for exploring limits and concepts for nano-enabled solar cells

“…89 Polarization-resolved EQE spectra for devices fabricated from such rectangular NWs reveal several new features. In the TE spectrum of the 260 nm diameter NW ( Figure 11A, black straight), a peak centered at 570 nm shows a nearly-unity EQE amplitude, whereas bulk Si would require ~3.3 µm of material to produce the same EQE value at this wavelength.…”

Diffusion pathways of phosphorus atoms on silicon (001)

“…The reaction of phosphine with silicon (001) has been extensively studied using numerous experimental techniques including STM 8,9,[14][15][16][17][18][19] , temperature programmed desorption [20][21][22][23][24][25] , low energy electron diffraction 20,24 , and several kinds of spectroscopy 9, 16,17,26,27 . Extensive theoretical modeling 19,[28][29][30][31][32][33] in conjunction with detailed STM images provided a consistent interpretation of the first stage of this reaction, namely the thermal dissociation of PH 3 into phosphorus and hydrogen adatoms.…”