Crystalline Properties and Strain Relaxation Mechanism of CVD Grown GeSn

Abstract

The crystalline properties of strained and strain-relaxed CVDgrown GeSn layers were investigated. A positive deviation from Vegard's law was determined, resulting in the extraction of a new experimental bowing parameter for GeSn: b GeSn = 0.041 Å (in excellent agreement with recent theoretical predictions). The GeSn critical thickness for strain relaxation as a function of Sn concentration was determined, resulting in significantly higher values than those predicted by equilibrium models. A composition-dependent strain relaxation mechanism was also found, with the formation of an increasing density of GeSn pyramidal islands in addition to misfit dislocations at lower Sn concentration.

Amorphous inclusions during Ge and GeSn epitaxial growth via chemical vapor deposition

“…However, we also observed that when the thickness of these layers increases, their surface is increasingly covered by islands, which we initially attributed to strain relaxation [7]. In this work, we investigate in more details the characteristics of these islands and we discuss the presence of an amorphous core inside them.…”

“…Low temperature growth processes are often required in order to fabricate Ge or GeSn heterostructures without undesired strain relaxations, elemental intermixing, dopant diffusion or Sn precipitation [5]. However, low-temperature growth is known to have a series of possible undesired consequences, such as the roughening of the surface [6], the formation of defects or the inclusion of localized or extended amorphous regions [6][7][8] (often referred to as epitaxial breakdown).…”

GeSn/Ge heterostructure short-wave infrared photodetectors on silicon

“…In theory, these materials can be used to achieve a direct energetic transition in a lattice-matched heterostructure grown on a Si substrate [1][2]. Even though the lattice mismatch between Ge and Sn is large, recent progress in growth has been reported, showing the realization of a fully strained Ge 0.92 Sn 0.08 layer on Ge [3][4]. This technological development allows evaluating the emission and absorption properties of these lattice-matched heterostructures.…”

Epitaxy and photoluminescence studies of high quality GeSn heterostructures with Sn concentrations up to 13 at.%

“…The peak of the roughly 2.5 µm thick Ge buffer lies below the cubic lattice line indicating a weak tensile strain of 0.16 %, whereas the GeSn peak is on the pseudomorphic line, proving that its growth was pseudomorphic on the Ge-VS underneath. A large compressive strain of about -1.9 % is obtained by using the bowing corrected Vegard´s law [8]. Room temperature photoluminescence measurements of these highly strained layers are presented in Fig.…”