Ex situ n⁺ doping of GeSn alloys via non-equilibrium processing

Abstract

Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p-and n-type doped regions for both planar and tridimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1×10 19 cm −3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3×10 15 cm −2 and electron concentration of about 4×10 19 cm −3 . The optical and structural properties of ionimplanted GeSn layers are comparable with the in situ doped MBE grown layers.

Strain and Band-Gap Engineering in Ge - Sn Alloys via P Doping

“…The E 0 critical point in GeSn alloys is significantly red-shifted in comparison with bulk Ge. In general, the red shift of E 0 with increasing P concentration is expected which would indicate a band gap narrowing in heavily doped n-type GeSn similarly to what happens in highly doped n-type Ge [44,45]. However, the occurrence of the Burstein-Moss effect cannot be fully discarded for heavily doped GeSn layers.…”

Electron Concentration Limit in Ge Doped by Ion Implantation and Flash Lamp Annealing

“…Using the formula ∆ω = −ω Ge = c × x Sn where c is the constant −82.8 (taken from Ref. 23), x Sn is Sn concentration, ω GeSn and ω Ge are the transverse optical (TO) phonon mode position in GeSn and bulk-Ge, respectively, and, while assuming fully relaxed layer, we can calculate the Sn concentration. Based on the Raman spectrum, the Sn concentration in presented film is in the range of 2.4%, which is much higher than expected from implantation parameters.…”

“…Since we know the Sn concertation from independent methods (in this sample Sn concentration is 1.5%), using Raman spectroscopy it is possible to estimate the strain in the layer while using formula ∆ω = a × x Sn + b × ε, where ε is the strain, a = −83.11 and b = −374.53 (after Ref. [23]). According to the calculation, the honeycomb structure that is presented in Figure 1f is tensile strained, with ε = 0.86%.…”

“…P-dimers in Ge are deep donors and P-clusters are electrically not active. The transverse optical (TO) phonon mode in intrinsic Ge is observed at 300.5 cm −1 [23], which means that the test sample is fully relaxed. After P-doping, the TO phonon mode moves significantly towards the lower wavenumber and the full width at half maximum (FWHM) increases.…”

Tin-based donors in SiSn alloys

“…Some studies have investigated extrinsic doping of Sn-containing alloys. [16][17][18][19][20] However, in general it is tacitly assumed that Sn itself is electrically inactive, as it is an isovalent species to Si and Ge. Indeed, the only Sn-related electrically active defect detected in early studies of Sn-doped Si was Sn-vacancy (SnV) pairs after irradiation.…”