Structural properties of relaxed thin film germanium layers grown by low temperature RF-PECVD epitaxy on Si and Ge (100) substrates

Abstract

International audienceWe report on unusual low temperature (175 °C) heteroepitaxial growth of germanium thin films using a standard radio-frequency plasma process. Spectroscopic ellipsometry and transmission electron microscopy (TEM) reveal a perfect crystalline quality of epitaxial germanium layers on (100) c-Ge wafers. In addition direct germanium crystal growth is achieved on (100) c-Si, despite 4.2% lattice mismatch. Defects rising from Ge/Si interface are mostly located within the first tens of nanometers, and threading dislocation density (TDD) values as low as 106 cm−2 are obtained. Misfit stress is released fast: residual strain of −0.4% is calculated from Moiré pattern analysis. Moreover we demonstrate a striking feature of low temperature plasma epitaxy, namely the fact that crystalline quality improves with thickness without epitaxy breakdown, as shown by TEM and depth profiling of surface TDD

Heteroepitaxy of High-Mobility Germanium on Sapphire (0001) with Magnetron Sputtering

“…Factors resulting in a rough surface after 850 °C post annealing include germanium film surface recrystallization, evaporation of the Ge at high temperature, and formation of volatile monoxide as mentioned above. A germanium film grown on a silicon substrate generally results in a rough surface under the Stranski–Krastanov growth mode due to the large lattice mismatch, , and the post-annealing step normally worsens the situation. It will be a worse-case scenario for germanium films grown on the sapphire substrate due to their significantly larger lattice mismatch.…”

“…It will be a worse-case scenario for germanium films grown on the sapphire substrate due to their significantly larger lattice mismatch. The low-temperature multiple-step CVD germanium epitaxy on silicon can be used to reduce the surface roughness to less than 1.0 nm ,, but could often have a trade-off of lower crystal quality. To reduce the surface roughness, commonly used techniques in the device fabrication process include the use of a capping layer (such as SiO 2 or Si 3 N 4 ) to effectively control the material loss during the post-annealing step , or a standard chemical mechanical polishing (CMP) process to smoothen the surface.…”

Advances in the development of high efficiency III-V multijunction solar cells on Ge|Si virtual substrates

“…III-V structures are grown by metal-organic chemical vapor deposition (MOCVD) using standard precursors [3]. Thick Ge layers are deposited by reduced pressure chemical vapor deposition (RP-CVD) [3] and ultrathin Ge films are deposited by radio-frequency, plasma-enhanced chemical vapor deposition (RF-PECVD), using the process parameters explained elsewhere [4]. 0.1 cm 2 solar cells are manufactured using standard photolithography techniques and gold-based metal stacks, except for Si that uses a Pd/Ti/Pd/Al system (details in [1]).…”

One-Step Cost-Effective Growth of High-Quality Epitaxial Ge Films on Si (100) Using a Simplified PECVD Reactor

“…The high temperatures involved have the potential to adversely affect films with low thermal budgets used in the device process flows [14]. A low temperature single step deposition process solves these challenges as it leads to significant cost reduction and limits the thermal strain arising from the difference in thermal coefficients of expansion between Ge and Si [15]. For the aforesaid reasons, Ge film growth at relatively lower temperatures (<400 • C) were studied in this work.…”

“…Radio-frequency (RF) discharge-based PECVD utilizes the capacitive coupling between the electrodes, which excites the precursor gases, induces a chemical reaction, and results in the deposition of the reaction products [18]. PECVD is known to provide a higher film deposition rate compared to conventional CVD through the interaction of the precursor sources with the highly energetic ions and radicals generated in the plasma [13,15,19]. In this work, Ge films were deposited using an in-house assembled simplified RF PECVD reactor by the use of the substrate-electrode direct-contact approach described above.…”