Surface Passivation for InAs and InAs/InAsSb T2SL photodetectors
Vicky W. Zhang, Henry Yuan, Jongwoo Kim, Carl Meyer, Devon Myers, Eli Sullivan, Witold Czelen, Chris Giranda, Gary Apgar, Mike R. Meixell, Desiree Calhoun, Jeremy Palmer, Paul Mark, Mark Bracey, Joyce Laquindanum, Ravi Guntupalli
Teledyne Judson Technologies
Background
InAs and InAs/InAsSb type-II superlattice (T2SL) photodetectors are critical for mid-wave infrared (MWIR) applications including imaging, spectroscopy, and space sensing. The performance, stability, and yield of these detectors are highly sensitive to surface passivation, which mitigates surface recombination, reduces interface traps, minimizes sidewall leakage, and protects against oxidation. Passivation also provides better control of Fermi-level pinning, improving the overall electrical and optical performance of discrete detectors and focal plane arrays (FPAs).
Challenge
Native oxides on InAs and InAs/InAsSb surfaces, such as As₂O₃ and In₂O₃, are unstable and prone to corrosion, releasing toxic components that are particularly problematic for biological and high-reliability applications. In addition, improper surface passivation can increase leakage current, reduce shunt resistance, and degrade spectral response. Conventional SiO passivation has limitations including suboptimal hydrophobicity, modest thermal stability, and less effective optical performance. Achieving uniform, thermally stable, and optically optimized passivation while maintaining or enhancing electrical performance has been a persistent challenge.
Figure 1: TJT T2SL BB ARC uniformity, with thickness uniformity on the left and index uniformity on the right. Each test is done over 4 inch test wafers, demonstrating very good uniformity.
Solution
A new surface passivation process was developed that simultaneously serves as an anti-reflection coating (ARC) optimized for the MWIR spectral range. Multiple techniques were explored, including polymer encapsulation, atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), thermal evaporation, and surface treatments. Experimental design optimized key parameters such as junction depth, mesa height, passivation layer thickness, surface roughness, and uniformity over 4-inch wafers.
The optimized polymer passivation demonstrated high thermal stability, low surface wetting, and enhanced hydrophobicity, improving contact angle by up to 50 %. The ARC functionality reduces reflection and improves spectral response, with peak transmission achieved in the 3-5 µm range for T2SL detectors. Surface treatment and post-thinning processes further enhanced uniformity without compromising optical transmission (>95 % up to 12 µm wavelength).
Results
Electrical Performance: Passivated InAs detectors exhibited consistent dark current and improved shunt resistance across different mesa heights and junction depths. Shallow to medium mesa heights with optimal junction depth were identified as favorable for minimizing leakage while maintaining pixel isolation. I–V and R–V characteristics remained stable or slightly improved after passivation, thinning, and surface treatment.
Optical Performance: Both InAs and InAs/InAsSb T2SL detectors achieved significantly enhanced responsivity and quantum efficiency (QE) after passivation. ARC-optimized coatings improved spectral response uniformity without degradation. Surface treatment had minimal impact on responsivity, and prolonged or aggressive treatment was avoided to prevent reductions in QE.
Surface Properties: Atomic force microscopy (AFM) revealed that thinned and treated polymer passivation doubled surface roughness compared to native surfaces, which enhanced hydrophobicity and contact angle stability. Multiple measurements across wafers confirmed excellent uniformity of surface treatment and passivation thickness.
MWIR T2SL Detectors: Two TJT designs with different barrier materials (AlAsSb and AlGaAsSb) showed targeted 50 % cutoff wavelengths ranging 4.85–5.7 µm across operating temperatures (150 K to room temperature). Passivation and ARC design yielded high hydrophobicity and spectral response enhancement over the entire MWIR band. Uniformity measurements indicated consistent thickness and index across 4-inch wafers, supporting reproducible fabrication for FPAs.
Conclusion
The optimized passivation process significantly improves InAs and InAs/InAsSb T2SL detector performance, stability, and yield. Key outcomes include enhanced surface hydrophobicity (contact angle improvement up to 50 %), robust electrical performance across mesa geometries, and increased responsivity and QE through ARC integration. The process achieves uniform, thermally stable passivation suitable for both frontside and backside illuminated detectors, enabling high-performance MWIR photodetectors and FPAs with improved long-term reliability and optical efficiency.
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Surface passivation for InAs and InAs/InAsSb T2SL photodetectors
Vicky W. Zhang, Henry Yuan, Jongwoo Kim, Carl Meyer, Devon Myers, Eli Sullivan, Witold Czelen, Chris Giranda, Gary Apgar, Mike R. Meixell, Desiree Calhoun, Jeremy Palmer, Paul Mark, Mark Bracey, Joyce Laquindanum, Ravi Guntupalli
Abstract
InAs has drawn a lot of attention for high performance transistors, optical applications, and chemical sensing due to its narrow band gap and very high near surface electron mobility. It has been also widely used for type II superlattice and avalanche photodiode arrays and is one of the standard materials used for mid-wavelength infrared (MWIR) photodetectors. One technical challenge for InAs related applications is to overcome the highly leaky InAs and passivation interface and achieve high stability surface passivation layer over InAs. The successful development of a new surface passivation process that is suitable for Teledyne Judson Technology (TJT) InAs mesa photodetectors was reported in previous work. This passivation did not cause InAs detector performance degradation and showed good stability and process compatibility with the detector assembly/packaging processes. In this paper, the extensive study of key process parameters optimization, including junction depth, trench height, passivation layers thickness, surface roughness and thinning process tailoring, will be covered. Characterization on InAs and InAs/InAsSb T2SL MESA and passivation quality were then performed. Optical and electrical characterizations of detector performance have been conducted, and the results have been analyzed and compared with TJT conventional InAs products, including dark current, shunt resistance, spectral responsivity, QE, and spatial photo-response uniformity over various temperatures. Passivation surface tension, which is essential for device surface condensation control and long-term stability, has also been investigated and compared for different processes. Wafer level and packaging level yield comparison between this newly development vs. process of record (POR) was also reported. By optimizing the passivation process, the significantly improved device performance stability and yield have been achieved and presented in this paper. In addition, the new surface passivation layer also serves as an anti-reflection coating (ARC) that enhances the InAs as well as the InAs/InAsSb T2SL detector spectral response and QE when optimized to the wavelength of interest for frontside illuminated detectors. Broad band ARC design for InAs/InAsSb T2SL backside illuminated focal plan array under TJT development has also been performed and discussed in this work.
Reference
Vicky W. Zhang, Henry Yuan, Jongwoo Kim, Carl Meyer, Devon Myers, Eli Sullivan, Witold Czelen, Chris Giranda, Gary Apgar, Mike R. Meixell, Desiree Calhoun, Jeremy Palmer, Paul Mark, Mark Bracey, Joyce Laquindanum, and Ravi Guntupalli, (29 May 2025) Surface passivation for InAs and InAs/InAsSb T2SL photodetectors, Proc. SPIE 13469, Infrared Technology and Applications LI, 1346912; https://doi.org/10.1117/12.3056058
