Strain Modulation of Selectively and/or Globally Grown Ge Layers

Abstract

This article presents a novel method to grow a high-quality compressive-strain Ge epilayer on Si using the selective epitaxial growth (SEG) applying the RPCVD technique. The procedures are composed of a global growth of Ge layer on Si followed by a planarization using CMP as initial process steps. The growth parameters of the Ge layer were carefully optimized and after cycle-annealing treatments, the threading dislocation density (TDD) was reduced to 3 × 107 cm−2. As a result of this process, a tensile strain of 0.25% was induced, whereas the RMS value was as low as 0.81 nm. Later, these substrates were covered by an oxide layer and patterned to create trenches for selective epitaxy growth (SEG) of the Ge layer. In these structures, a type of compressive strain was formed in the SEG Ge top layer. The strain amount was −0.34%; meanwhile, the TDD and RMS surface roughness were 2 × 106 cm−2 and 0.68 nm, respectively. HRXRD and TEM results also verified the existence of compressive strain in selectively grown Ge layer. In contrast to the tensile strained Ge layer (globally grown), enhanced PL intensity by a factor of more than 2 is partially due to the improved material quality. The significantly high PL intensity is attributed to the improved crystalline quality of the selectively grown Ge layer. The change in direct bandgap energy of PL was observed, owing to the compressive strain introduced. Hall measurement shows that a selectively grown Ge layer possesses room temperature hole mobility up to 375 cm2/Vs, which is approximately 3 times larger than that of the Ge (132 cm2/Vs). Our work offers fundamental guidance for the growth of high-quality and compressive strain Ge epilayer on Si for future Ge-based optoelectronics integration applications.

Dual-Step Selective Homoepitaxy of Ge with Low Defect Density and Modulated Strain Based on Optimized Ge/Si Virtual Substrate

“…It should be mentioned here that the thin Al 2 O 3 layer was used to stabilize the RPCVD prepared SiO 2 layer, whose density is lower compared to the thermal furnace method. The detailed growth procedures, from step 1 to step 8, as shown in Figure 1 , are described in our previous work which is aimed at preparing a type of Ge/Si film structure with compressive strain that is preferable for p-MOS fabrication [ 43 , 44 ]. After the formation of the 2nd Ge epilayer, we repeated the 4–8 steps to grow the 3rd Ge layer.…”

Review of Ge(GeSn) and InGaAs Avalanche Diodes Operating in the SWIR Spectral Region

“…Firstly, TDDs in the Ge absorption layer are still high. To eliminate the TDDs, numerous strategies were proposed in recent decades, including doped Ge buffer layers [ 108 , 109 , 110 ], compositionally graded SiGe buffer layers [ 111 , 112 , 113 ], ultra-thin Si/SiGe superlattice buffer layers [ 114 , 115 ], high temperature annealing [ 116 , 117 , 118 ], three-step growth [ 119 , 120 ], the selective epitaxial growth (SEG) method [ 121 , 122 , 123 ], etc. With the continuous effort focused on decreasing the TDDs in the Ge layer, the TDDs for the top Ge layer were evaluated to be in the orders of 10 6 –10 7 cm −2 .…”

Review of Highly Mismatched III-V Heteroepitaxy Growth on (001) Silicon

“…From the peak position of RSM, the in-plane strain ε ‖ of the GaAs and Ge layer were calculated from the extracted calculation of the in-plane lattice constant and out-of-plane lattice constant of the GaAs and Ge. Compared with the lattice constant of bulk GaAs and Ge, the residual thermal strain of Ge is about 89.8% lower than that of the Ge layer on normal Si substrates [ 140 ]. The residual thermal strain of GaAs is 29.4% lower than that of the GaAs layer grown on the Ge/Si template [ 141 ].…”