Hydrogenation for defect passivation in (Si)GeSn alloys

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Space Technology The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: The objective of this topic is to evaluate the extent to which the background carrier concentration and the minority carrier lifetime of (Si)GeSn semiconductor alloys can be improved by post growth hydrogenation. DESCRIPTION: Incorporation of Sn into either Silicon or Germanium semiconductors causes a reduction of the bandgap and indirect/direct transition around 8% Sn for GeSn alloys. Tunability of the material system has shown coverage of the short- to mid-wave infrared wavelength spectrum (2.0 to 8.0 micrometers). Couple the tunability with large area substates (8 inch Silicon) and mature CMOS processing technology; the ingredients for high performance, high manufacturability photodetection are available. As of this year the minority carrier lifetime has been shown to be short (~3 ns) with a high background carrier concentration as a limiter to device performance [1]. This recent demonstration of minority carrier lifetime in GeSn/SiGeSn quantum well is significant because the lifetime reflects how long charge excited by incoming infrared radiation can transport in the material before it can no longer be collected by the EO/IR system, i.e. the likelihood that the photon is seen. Long lifetime lead to efficient collection of charge and low dark currents, two key attributes of an efficient, high signal-to-noise image sensor. While other measures of performance are associated with the material's fundamental nature (e.g. mobility, absorption, ect.), lifetime is fundamentally a measure of concentration of defects in the material and thus the lifetime is improved by innovation and advances in material synthesis (i.e. defects add to the background carrier concentration). As discussed in greater detail in Ref.1, the challenge to further improving (Si)GeSn for infrared-sensing applications is that low growth temperatures increase the incorporation of defects and higher growth temperatures significantly inhibit the incorporation of Sn. Increasing the growth temperature shortens the maximum cutoff of the materials as Sn, the element responsible for reducing the bandgap, incorporates less efficiently. The path forward for (Si)GeSn will require either a novel growth approach that enables more effective incorporation of Sn in (Si)GeSn at higher growth temperatures where the background carrier concentration/minority carrier lifetime can be optimized, or a means of passivating defects present in (Si)GeSn alloys grown at lower growth temperatures wither Sn incorporates more efficiently. This topic seeks to evaluate post-growth hydrogenation as a means to passivate defects and improve the background carrier concentration/minority carrier lifetime in low-temperature grown (Si)GeSn alloys. Hydrogenation is commonly used to passivate defects in a multitude of semiconductor materials that suffer from defects. Given that the lifetime has been shown to depend on the growth conditions utilized to synthesize the material, it is possible that the defects introduced at lower growth temperatures can be passivated, leading to lower background carrier concentrations and longer minority carrier lifetimes in (Si)GeSn alloys with sufficient Sn mole fraction to effectively cover the short- to mid-wave infrared spectrum. PHASE I: Awardee(s) will develop a hydrogenation recipe and test plan. Materials to be tested will be provided by the TPOC at AFRL/RVSU. Other materials suffering from non-optimal growth temperature constraints identified by the proposers may be included as well. PHASE II: Awardee(s) will execute hydrogenation experiments. Hydrogenated materials will be returned to AFRL/RVSU for background carrier concentration/minority carrier lifetime testing and evaluation. An iterative process to optimize the hydrogenation technique will be performed. PHASE III DUAL USE APPLICATIONS: If a successful hydrogenation recipe is identified, the process may be commercialized and utilized to improve (Si)GeSn and other optoelectronic materials that suffer from non-optimal growth conditions constraints. REFERENCES: P.C. Grant, P.T. Webster, R.A. Carrasco, C.P. Hains, N. Gajowski, S.-Q. Yu, B. Li, C.P. Morath, D. Maestas,"Auger Limited Minority Carrier Lifetime in GeSn/SiGeSn Quantum Well" Appl. Phys. Lett. (under review, Nov. 2023); KEYWORDS: Hydrogenation; GeSn; SiGeSn