Boron and Phosphorous Doping of GeSn for Photodetectors and Light Emitting Diodes

Abstract

With an electrically pumped group IV laser operating at room temperature as a long term goal, we would like to replace the boron and phosphorous doped Ge layers used in previous pin structures with GeSn:B and GeSn:P. We have thus investigated the in-situ doping of GeSn with Ge2H6, SnCl4, B2H6 (p-type) or PH3 (n-type) at 349°C, 100 Torr on Ge Strain-relaxed Buffers, themselves on Si(001) substrates. The Sn content from Wavelength Dispersive X-Ray Fluorescence (WDXRF) was constant around 6.5% for low F(B2H6)/F(Ge2H6) and F(PH3)/2*F(Ge2H6) Mass-Flow Ratios (MFRs). It fell down to 4.6% (GeSn:B) and 5.6% (GeSn:P) for higher MFRs. This drop was likely due to the dopant precursors that catalyzed the Ge Growth Rate component. Substitutional B and P contents were extracted from the differences between real Sn contents from WDXRF and “apparent” Sn contents from X-Ray Diffraction (compressive strain compensation by small B and P atoms). The B substitutional concentrations increased sub linearly with the MFR, reaching values of at most 5.2x1019 cm-3. Meanwhile, the P substitutional concentration increased linearly with the MFR, up to 2.2x1020 cm-3. WDXRF gave us also access to the atomic P concentrations, with values as high as 2.2x1020 cm-3 A cross-hatch along <110> was otherwise present on the surface of the various GeSn:B and GeSn:P layers, which were rather smooth. Only the GeSn:B layers grown at the three highest MFRs exhibited some B and/or Sn surface segregation.