Building on our previous efforts, IQE will demonstrate the high-volume manufacturability of our MBE growth process for GaSb-based MW and LW infrared photodetectors (IRPDs) structures. This work focuses on the ability to scale across multiple MBE reactor platforms and across multiple production sites. Supporting the scaling of FPAs requires the ability to grow IRPD structures on larger diameter substrates with good wafer-to-wafer and cross-platen uniformity. Enhancement of Ga-free LWIR QE may be realized through metamorphic growths and the use of high-index substrates. We have also extended our heteroepitaxial growth effort on Si substrate from bulk InAsSb to Sb T2SL MWIR structures.
In recent years GaSb-based infrared (IR) photodetector technology has continued to mature, moving from research and development to production-scale manufacturing for a variety of applications. In parallel, maturation of molecular beam epitaxial (MBE) growth of MWIR and LWIR photodetectors has allowed for the ramp to production volumes. Recent developments at IQE have shown that our epitaxial process is not only transferrable to production-scale reactors at the same manufacturing site, but to reactors across IQE production sites. Following the demand for larger focal plane arrays (FPAs), IQE has demonstrated high quality epitaxy grown on GaSb substrates measuring 76.2 mm to 150 mm (3” to 6”) diameter without sacrificing cross-wafer uniformity. IQE’s ability to ramp this process to a production-scale MBE, allowing for 9100 mm wafers per run, has resulted in increased throughput, volume, and yield. The surface morphology of these materials will be measured by Surfscan, AFM, and Nomarski optical microscope; the crystalline properties evaluated via HRXRD; and, using large-area mesa diodes, device performance (dark current, QE, and cutoff wavelength) will be analyzed. Using the same material and device characterization techniques, we will assess the wafer-to-wafer cross-platen uniformity, imperative for high-yield production. Through material and device characterization of each production run, IQE is able to implement statistical process control techniques to improve consistency, yield, and throughput. This will demonstrate the production readiness of IQE’s IR epitaxy.
MBE and MOVPE growths of InP-based extended wavelength and GaSb-based IR emitter and detector structures have progressed to production mode. These photonics device structures are typically grown using large format, multi wafer MBE and MOCVD tools and on large diameter substrates (100 to 150 mm). In this work, material characterization data of advanced InP- and GaSb based epitaxial structures will be shown. Multi point measurements showing cross-wafer and cross-platen uniformity will also be shared. Finally, detailed analysis of run-to-run epiwafer data will be presented to demonstrate the manufacturability of our production epitaxial process for these advanced photonics device structures.
After years of progress, GaSb based mid-wave infrared (MWIR) devices have moved from development into manufacturing. To accommodate this maturation, the Molecular Beam Epitaxy (MBE) growth of the MWIR photodetector structures has progressed to a production mode. By necessitating many repetitions of a given growth structure, the increase in volume has enabled the use of Statistical Process Control (SPC) techniques to improve command over critical parameters, and thereby improve the yield and throughput. These products have been grown on GaSb substrates using large format, multi-wafer platens for 100 mm and 125 mm diameter substrates in a Veeco Gen2000 MBE system. The material properties were measured by Atomic Force Microscopy (AFM), High-Resolution X-Ray Diffraction (HRXRD), Photoluminescence (PL), and diode performance (turn-on voltage, dark current (JD), Quantum Efficiency (QE), and cutoff wavelength). Analysis of the run-to-run data will be presented to exhibit the manufacturability of these structures.
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.
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.
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 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.
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