Low temperature epitaxy of germanium-tin semiconductor heterostructures on silicon

Ge1-ySny binary alloy is an intriguing group IV semiconducting material which offers energy bandgap engineering by modifying its Sn concentration, indirect-to-direct bandgap transition with Sn concentration of 6–11 at.%, strain engineering by controlling its thickness and Sn concentration, interface improvement, defect prevention, and temperature reduction in the process of epitaxial growth. There have been several achievements in the development of Ge1-ySny optoelectronic devices, such as IR LEDs, IR LASER, and IR photodetectors with high efficiency. There are other exciting potential Ge1-ySny electronic and quantum applications, such as MOSFET with high mobility, TFET with low energy consumption and high performance, IR wave guides, and spintronics. However, to further develop Ge1-ySny applications and devices, it is essential to fully understand the epitaxy and material properties. In this research, the heteroepitaxial growth of Ge1-ySny on a Si (001) substrate via a relaxed Ge virtual substrate using CVD with either of GeH4 or Ge2H6, in combination with SnCl4. It is demonstrated that Sn segregation and precipitation are controlled when GeH4 is used over Ge2H6, under very similar growth conditions, which is crucial for the growth of monocrystalline Ge1-ySny thin films. Contrary to previously reported results, the GeH4 could indeed be a viable Ge precursor for epitaxy of superior quality Ge1-ySny epilayers at very low cost. In addition, the growth of fully strained Ge1-ySny epilayers with a Sn concentration of over 13 at.% at a very low growth temperature when using GeH4 and SnCl4, which was previously assumed to be impossible, is successfully achieved. The lowest temperature at which epitaxial growth of Ge1-ySny can take place is estimated at ~231 °C, which is very close to the melting point of Sn. Moreover, since strain relaxation in Ge1-ySny epilayers affects their electrical and physical properties, it is therefore essential to investigate the mechanism of strain relaxation in Ge1-ySny epilayers. The effect of strain relaxation of compressive strained Ge1-ySny epilayers as a function of growth rate and Sn concentration is investigated. Additionally, a grading technique, in which the SnCl4/GeH4 ratio is tuned during the growth of Ge1-ySny epilayers, is demonstrated. It is shown how the grading technique can enable the growth of thick Ge1-ySny epilayers by suppressing Sn segregation. As a result, a relaxed Ge1-ySny epilayer with a higher quality and smoother surface is achieved. Furthermore, since doped Ge1-ySny epilayers could offer more flexibility to control physical, electrical, and optical properties over undoped ones, it is crucial to discover mechanisms that can control the incorporation of dopants into Ge1-ySny epilayers. The attempt of heteroepitaxial growth of both p- and n-type Ge1-ySny epilayers is examined. It is demonstrated that such attempt does not affect the quality of epilayers but influences their Sn concentration and growth rate. The attempt of incorporation of Si into Ge1-ySny (as known as Ge1-x-ySixSny) is also investigated. The incorporation of Si up to ~3 at.% into Ge1-x-ySixSny with a Sn concentration of ~9 at.% is successfully achieved. Finally, epitaxial growth of Ge\Ge1-ySny\Ge quantum well, Ge1-ySny\Ge multilayers, and Ge1-ySny\Ge1-zSnz (in which y ≠ z) is achieved. Epitaxial growth of the corresponding heterostructures, the investigation of the growth mechanisms, and the impact of CVD growth conditions on the quality of epilayers have been extensively carried out. These heterostructures could potentially offer greater flexibility in controlling the physical, electrical, and optical properties of Ge1-ySny related materials for device fabrication