Biaxial stress evaluation in GeSn film epitaxially grown on Ge substrate by oil-immersion Raman spectroscopy

Abstract

GeSn is being paid much attention as a next-generation channel material. In this work, we performed the excitation of forbidden transverse optical (TO) phonons from strained GeSn, as well as longitudinal optical (LO) phonons, under the backscattering geometry from the (001) surface by oil-immersion Raman spectroscopy. Using the obtained LO/TO phonons, we derived the phonon deformation potentials (PDPs), which play an important role in the stress evaluation, of the strained Ge1− x Sn x for the first time. The results suggest that PDPs are almost constant for the Ge1− x Sn x (x < 0.032). Biaxial stress calculated using the derived PDPs reasonably indicated the isotropic states.

Raman spectroscopy of group-IV Ge$_{1-x}$Sn$_{x}$ alloys: theory and experiment

“…3(d)), which is at the low end of the range of values reported in the experimental literature. [25][26][27][28][29]32,33,36,38,39,41,42 Test calculations for larger supercells containing up to 1728 atoms (not shown) yield minimal changes in ∆ω(x), confirming that the 512-atom supercells employed in our analysis are sufficiently large to allow for realistic analysis of disorder-related effects (since, in smaller supercells, Born-von Karman boundary conditions can introduce spurious short-range ordering which limits the ability to describe realistic disordered alloy microstructure 71 ).…”

“…39), which range from as low as b = 64 cm −1 to as high as 563 cm −1 , 25,28 with the majority of values estimated based on experimental data being at the higher end of this range. 32,33,36,38,39,42 To address the uncertainty associated with this important parameter, we compute b via both analytical and atomistic approaches.…”

Raman spectral shift versus strain and composition in GeSn layers with 6%–15% Sn content

“…In addition, all the reported a and b coefficients provided in Table I [16][17][18][19][20][21][22][23][24][25] have been added as dashed lines and our data linear fits are plotted as solid lines. [17][18][19][20][21]25,54 and strained layers 19,21,23,25,54 compared to experimental data from 58 and our work.…”

“…b=521 cm -1 ) is by contrast higher than previously reported coefficients (Table I) excepted for 19 which is the only study on thin GeSn layers grown on InGaAs SRBs. Differences with other works can be attributed to the use of thick annealed layers 23 or to the layer compositions 21,25,54 . For thick annealed layers (i.e.…”

“…0.147xSn 20,36 (Equation 2), generating a spectral shift proportional to xSn (Equation 3). Table I gives the reported Raman coefficients a, b and c available in the literature for GeSn alloys [16][17][18][19][20][21][22][23][24][25]54 . Note that the c coefficient in ref.…”