Effect of Strain on Room-Temperature Spin Transport in Si0.1Ge0.9

Abstract

We report a strain effect on spin transport in semiconductors that exhibit Ge-like conduction bands at room temperature. Using four-terminal nonlocal spin-transport measurements in lateral spin-valve devices, we experimentally estimate the spin diffusion length (λ) of Ge and strained Si 0.1 Ge 0.9 with two different carrier concentrations. Despite the Ge-like electronic band structure, the obtained λ of a strained Si 0.1 Ge 0.9 is comparable to that of a Si channel. We discuss a possible mechanism of the strain-induced enhancement of λ at room temperature. As a consequence, we demonstrate the electrical detection of 5-μm lateral spin transport in the strained Si 0.1 Ge 0.9 by applying an electric field at room temperature.

Local strain distribution analysis in strained SiGe spintronics devices

“…4(a), Sample 1 is found to have an average strain of about 0.4%-0.6% over a wide area of the sample. These values are close to the amount of strain expected from the lattice mismatch of 0.40% between Si 0.1 Ge 0.9 and Ge, and about 0.2% of tensile strain in the Ge buffer layer because of mismatch in thermal expansion coefficient between Ge and Si substrate, 6) suggesting that the spin diffusion length was enhanced by the application of strain as expected. The comparison between the channel area and the areas under the electrodes shows that strain is slightly smaller at the channel area, as observed in Sample 1.…”

“…In devices fabricated by the above method, significant improvement of the spin diffusion length is achieved. 6) On the other hand, different spin diffusion lengths have been observed in different devices, and the variation in the properties is problematic. This is possibly due to the unevenness of the applied strain or that the effects of crystal defects such as dislocations which may differ by devices.…”

“…In the previous study, we have succeeded in improving λ at RT by employing a Ge-rich SiGe spin transport layer formed on a Si (111) substrate by MBE. 6) This is achieved by intentionally applying strain to the SiGe layer to induce an energy splitting of the four degenerate valleys in the conduction band, 7,8) thereby suppressing inter-valley spinflip scattering which is the main cause of spin relaxation. 9) However, the actual strain applied to the SiGe spin transport layer in the form of device structures has not been evaluated, and the correlation between spin transport properties and strain or defect distribution has not been clarified.…”

Significant reduction of crack propagation in the strained SiGe/Ge(111) induced by the local growth on the depth-controlled area patterning

“…Thus far, pure spin-current transport has been observed in Ge(111) and SiGe epitaxial layers even at room temperature. [15][16][17] Recently, in the strained Si 0.1 Ge 0.9 layers, we clearly observed an enhancement in the spin lifetime at room temperature, 18) meaning that the strain induced in Si 0.1 Ge 0.9 enables us to lift the degeneracy between L-valleys in the conduction bands where the intervalley spin-flip scattering occurs. Since high-quality Ge-on-Si virtual substrates have recently become available owing to the two-step growth method, [19][20][21][22][23] feasibility of employment of SiGe with high Ge concentrations has remarkably increased.…”

Electric-field induced modification of the photoluminescence polarization in Ge/Si0.15Ge0.85 quantum wells

“…Spin manipulation is a crucial aspect for fundamental investigations and the future application of spin-based optoelectronics. 1 Within this field, group IV semiconductors have shown appealing properties such as long spin lifetime, [2][3][4][5][6][7] isotopic purification and compatibility with Si manufacturing processing. 8,9 For practical purposes, electrically-induced spin manipulation through the effect originally introduced by Rashba and Sheka 10 would be highly desirable.…”