Synthesis and optical properties of (GaAs)yGe5-2y alloys assembled from molecular building blocks

Abstract

Monocrystalline alloys of GaAs and Ge with compositions (GaAs)yGe5–2y have been synthesized following a chemical vapor deposition approach that promotes the incorporation of Ga and As atoms as isolated donor-acceptor pairs. The structural and optical properties show distinct behavior relative to (GaAs)1-xGe2x counterparts produced by conventional routes. Strong band gap photoluminescence is observed in the 0.5–0.6 eV range for samples whose compositions approach the GaAsGe3 limit for isolated Ga-As pairs. In such samples, the Ge-like Raman modes appear at higher frequencies and are considerably narrower than those observed in samples with higher Ge concentrations. These results suggest that the growth mechanism may favor the formation of ordered phases comprising Ga-As-Ge3 tetrahedra. In contrast with the diamond-to-zincblende ordering transition previously reported for III-V-IV alloys, ordered structures built from Ga-As-Ge3 tetrahedra feature III-III and V-V pairs as third-nearest neighbors, and therefore both the III- and V-components are equally present in each of two fcc sublattices of the average diamond-like structure. These bonding arrangements likely lead to the observed optical response, indicating potential applications of these materials in mid-IR technologies integrated on Si.

Synthesis and Structural and Optical Properties of Ga(As1–xPx)Ge3 and (GaP)yGe5–2y Semiconductors Using Interface-Engineered Group IV Platforms

“…This trend is consistent with the behavior observed for the GaAsGe 3 compound, whose PL spectrum also contains a similar two-peak profile with energies similar to that of Ga­(P 0.20 As 0.80 )­Ge 3 , indicating that the emission wavelength does not change in any measurable manner by replacing As by P over a broad range up to x = 0.2. We note that this trend is reminiscent of the prior absorption measurements of (GaAs) x (Ge 2 ) 1– x alloys, which showed a nearly constant band gap energy of 0.5 eV as a function of Ge over a broad range of 30–70% . As in the case of GaAsGe 3 , IR spectroscopic ellipsometry also shows evidence for a direct optical transition (described below) at an energy close to the PL emission features in Figure .…”

“…We note that this trend is reminiscent of the prior absorption measurements of (GaAs) x (Ge 2 ) 1−x alloys, which showed a nearly constant band gap energy of 0.5 eV as a function of Ge over a broad range of 30−70%. 11 As in the case of GaAsGe 3 , IR spectroscopic ellipsometry also shows evidence for a direct optical transition (described below) at an energy close to the PL emission features in Figure 10. We also note that the PL peaks in this figure are consistently narrower than those we obtained for GaAsGe 3 .…”

“…Specifically, the use of Ga hydride precursors, in combination with P(SiH 3 ) 3 and As(GeH 3 ) 3 , allowed the exploration of the (GaP) y Si 5−2y and (GaAs) y Ge 5−2y alloy systems, respectively. 10,11 Epitaxial films of the former alloy was found to have increased absorption relative to crystalline Si in the visible portion of the spectrum, suggesting that it may be useful for solar cell applications. It was also found to have a lattice constant between that of GaP and Si, fairly close to the Vegard's law prediction of a linear average.…”

“…Recently, we have demonstrated a new approach for synthesizing hybrid III–V–IV alloys by utilizing custom-made chemical precursors that avoid the above issues by enabling the incorporation of preformed tetrahedral building blocks with direct III–V bonds into the growing crystal. − Although the initial work in this area made use of atomic beams of group III atoms, molecular sources have proved more successful for this purpose by enabling the synthesis of a broader range of alloy materials. Specifically, the use of Ga hydride precursors, in combination with P­(SiH 3 ) 3 and As­(GeH 3 ) 3 , allowed the exploration of the (GaP) y Si 5–2 y and (GaAs) y Ge 5–2 y alloy systems, respectively. , Epitaxial films of the former alloy was found to have increased absorption relative to crystalline Si in the visible portion of the spectrum, suggesting that it may be useful for solar cell applications. It was also found to have a lattice constant between that of GaP and Si, fairly close to the Vegard’s law prediction of a linear average.…”

Fabrication of Ge:Ga Hyperdoped Materials and Devices Using CMOS-Compatible Ga and Ge Hydride Chemistries

“…The compound is a colorless liquid with a vapor pressure of ∼1 Torr at room temperature, which makes it suitable for CVD experiments. [D 2 GaN­(CH 3 ) 2 ] 2 was recently utilized to fabricate a novel class of hybrid semiconductor compounds with compositions GaPSi 3 , GaAsGe 3 , and Ga 1– x P x Ge 3 by reactions of the compound with P­(SiH 3 ) 3 and As­(GeH 3 ) 3 between 370 and 500 °C. The [D 2 GaN­(CH 3 ) 2 ] 2 gas source delivers pure Ga atoms at low temperatures by eliminating robust D 2 and DN­(CH 3 ) 2 byproducts as described by the reaction The DN­(CH 3 ) 2 species is pumped away and does not participate in the growth process, leaving behind pure and crystalline epitaxial films devoid of C and N impurities.…”