As GaSb based LWIR nBn detector structures have progressed from development into production, the standard substrates have been 76.2 and 100 mm in diameter. Additionally, production growths on 125 mm substrates are gaining popularity. To meet demands for larger focal plane arrays (FPA), improve throughput, volume, and yield, IQE has made the next step in this progression. Our first demonstration of multi-wafer growth of 150 mm GaSb exhibited uniform, high quality MWIR epitaxy. In this work, we will share our results for the more challenging GaSb-based LWIR nBn detector structures. These growths were carried out on a large format platen (7 × 150 mm) by Molecular Beam Epitaxy (MBE). The material properties as measured by AFM, HRXRD, Nomarski microscope, and PL, along with diode performance (turn-on, QE, cutoff wavelength), will be presented. Using this data, we will analyze the wafer-to-wafer cross-platen uniformity. Additionally, we will compare the characterization and device results to similar structures grown on smaller diameter substrates, and consider the viability of utilizing 150 mm GaSb substrates for LWIR nBn detector structures.
We recently evaluated the optical and electric characteristics of mid-wave photodetector (PD) diodes grown on high-index substrates. Preliminary results indicate that substrate orientation and surface polarity can modify PD parameters such as photoluminescence (PL), dark current (Jd), quantum efficiency, and spectral characteristics. In this work, we focused on growth parameter optimization for long-wave type-II strained layer superlattice (T2SL) PD structures grown on (211)B and (311)A GaSb substrates. Material and PD diode characteristics were compared with reference data obtained on (100)-oriented substrates. Material quality was evaluated by HRXRD, AFM, Nomarski microscopy, 77 K PL, and PD J-V and spectral testing. Photoluminescence and cutoff wavelength measurements for diode structures fabricated on (211)B and (311)A substrates demonstrate a significant redshift due to a reduction of the optical bandgap in the SL. The extent of redshift increases with superlattice period and Sb mole fraction in the InAsSb layers in the absorber. All wafers demonstrated reasonable surface morphology without surface corrugation, with minor variability in roughness. Redshift in 77 K PL and cutoff wavelength, in combination with high QE and low Jd, obtained from growths on these high-index substrates offer a potential path to achieve enhanced PD characteristics with reduced SL period for a given wavelength by comparison to (100) substrates.
GaSb-based infrared (IR) photodetector technology progression is toward larger-format focal plane arrays (FPAs). This requires a performance-based and cost-based manufacturing process on larger diameter substrates for improved throughput, volume, and yield. IQE has demonstrated molecular beam epitaxy (MBE) growth processes for barrier-design detectors (nBn) in multi-wafer configurations on 4-inch and 5-inch diameter GaSb substrates, and via a metamorphic process on 4-inch and 6-inch GaAs substrates. Recently we took the next step in this progression, growing nBn detectors on 6-inch Si substrates coated with CVD-grown Ge, opening the door for potential integration with Si-based electronic circuitry. Here, we compare the epiwafer characteristics (morphology, x-ray, PL) and diode performance (turn-on, QE, cutoff wavelength) of this M-nBn on Ge-Si with the same M-nBn on GaAs and the corresponding nBn structure grown on native GaSb substrate. Similar performance was obtained on all three types of substrates. We also present FPA data based on a 640×512 pixel, 15 μm pitch process without substrate removal, where QE ~ 80%, NE▵T < 20 mK, and operability <99% was demonstrated. The results represent an important technological path toward next-generation large-format IR detector array applications.
GaSb and its heterostructures grown by molecular beam epitaxy (MBE) have received much attention given their application in a wide range of mid-wave and long-wave IR photodetector applications. With the maturation of the MBE growth process, focus is now turned to improving manufacturing readiness and the transition to the production of large-format wafers. We will discuss the transition from the development of early detector layer structures on 2” diameter GaSb substrates, through today’s 3”/4” production standard, and to the onset of 5” pilot production from the perspective of volume compound semiconductor manufacturing. We will report on the growth of 5” GaSb-based MWIR nBn detector structures using a large format 5×5” production MBE platform. Structural and optical properties, as well as electrical data from large-area mesa diodes will be presented and compared with results achieved with smaller batch size MBE reactor platform.