Development of Light Emitting Group IV Ternary Alloys on Si Platforms for Long Wavelength Optoelectronic Applications

Abstract

This paper describes preparation of a new class of Ge 1−x−y Si x Sn y direct-gap semiconductors grown on Ge-buffered Si substrates via depositions of trigermane (Ge 3 H 8 ), tetragermane (Ge 4 H 0 ), tetrasilane (Si 4 H 10 ), and stannane (SnD 4 ) hydride precursors. These react at ultralow temperatures 320−290 °C to produce thick (∼500 nm) monocrystalline films with concentrations closely reflecting the gas phase molar ratio of the coreactants. A series of Ge-rich samples with a fixed 3−4% Si content and progressively increasing Sn content in the 4−10% range are grown to explore the possibility of obtaining direct gap materials for the first time in this semiconductor system. The resultant films also exhibit residual compressive strains that are largely relaxed via rapid thermal annealing between 550 and 700 °C depending on composition. These temperatures are 50−75 °C above the thermal decomposition threshold of Ge 1−y Sn y /Ge materials with same Sn content, indicating that the ternaries are significantly more robust than the binary analogues. The compositional dependence of the strain relaxations is similar to that found for Ge 1−x Si x alloys grown directly on Si. Cross hatch patterns are formed on the surface of these materials as a consequence of interface misfit dislocations generated due to the mismatch with the underlying Ge buffer. The annealed films exhibit low defect densities and atomic scale chemical uniformity as indicated by STEM and element-selective EELS mapping, allowing a meaningful study of the optical properties as a function of Sn concentration. The results show that the separation of the direct and indirect edges can be made smaller than in Ge even for the non-negligible 3−4% Si content, confirming that with a suitable choice of Sn compositions the ternary Ge 1−x−y Si x Sn y reproduces all features of the electronic structure of the binary Ge 1−y Sn y , including the sought after indirect-to-direct gap cross over. The alloys produced in this study represent an attractive alternative to Ge 1−y Sn y for applications in IR optoelectronic technologies requiring high thermal budget processing and harsh operating conditions due to their enhanced thermal stability conferred by the incorporation of Si in the diamond-like structure.

SiGeSn Ternaries for Efficient Group IV Heterostructure Light Emitters

“…The low (<1 at%) solid solubility of Sn in Ge requires the use of very low growth temperatures (below about 400 °C), limiting the thermal budget for future device processing . However, the incorporation of Si atoms in GeSn to form ternaries is believed to enhance thermal stability, making them more robust and suitable for device applications, compared to their binary counterparts . From a theoretical point of view, calculation of SiGeSn band structures and alignments relies, amongst others, on bowing parameters for direct and indirect bandgaps, with a wide variation of values reported in different studies …”

“…In Figure b we also included b SiSn , extracted from refs. and . Comparing samples with a low and constant Si content, a clear decline of b SiSn with increasing Sn concentration can be observed.…”

Optical properties of Ge-richGe1−xSixalloys: Compositional dependence of the lowest direct and indirect gaps

“…An additional approach to the spectroscopy of the E 0 transition in Ge-rich materials is room temperature photoluminescence (PL). [19][20][21][22][23][24] Emission from E 0 is very weak in bulk Ge crystals due to reabsorption, [25][26][27] but becomes the strongest feature in micron-thick films. Accordingly, we now extend these studies to Ge 1-x Si x alloys, where the increasing separation between E 0 and the lowest indirect transitions should lead to a weakening of the E 0 signal, a trend that is confirmed by our experimental data.…”

High Resolution EELS Study of Ge1-ySny and Ge1-x-ySixSny Alloys

“…Observation of the Ge 1-x-y Si x Sn y /Ge interface in Figure 3 reveals that the Sn distribution is uniform throughout the layer. Figure 4 shows that the Sn atoms occupied Ge lattice columns as evidenced by atomic resolution EELS maps from a sample volume of 4x4 nm 2 in the lateral direction and a thickness of 25-30 nm [5]. Further work to be reported at the meeting will include electronic structure characterization and band gap determination obtained from EELS.…”