Aadil Waseem

Al-rich AlGaN is essential for ultra-wide-bandgap (UWBG) electronics and deep-ultraviolet optoelectronics, yet its processing is limited by the lack of damage-free etching methods. Plasma-based approaches introduce defects, while anisotropic wet etching for GaN often fails at high Al content due to the larger bandgap and stable oxide formation. Here, we demonstrate the first, to our knowledge, plasma-free hν-MacEtch of Al0.6Ga0.4N using a modified HF/(NH4)2S2O8 chemistry that enables stable etching and remains compatible with GaN, allowing a single process across AlGaN/GaN heterostructures. Ohmic contacts formed on hν-MacEtched surfaces show comparable contact resistance but significantly improved uniformity (15% using inductively coupled plasma reactive ion etching). These results establish a viable pathway for damage-free, reproducible processing of UWBG nitride materials and devices.

Chemically robust III-nitrides (III-N) with bandgaps in the visible spectral range are critical for advancing emerging technologies such as solar-driven photocatalysis and optoelectronics. Conventional methods for bandgap reduction of GaN, such as increasing indium content in InGaN alloys, are limited by lattice mismatch strain-induced defects that compromise device performance. Incorporating small number of anions like arsenic (As) or antimony (Sb) offers an alternative through significant band bowing in GaN; however, achieving high visible emission efficiency remains challenging for in situ epitaxial incorporation due to thermodynamic barriers of limited solubility. This study demonstrates high-temperature (550 and 1000 °C) ion implantation as an effective strategy to tailor the spectral response of various GaN semiconductor structures into the visible range, achieving bright room-temperature photoluminescence at ∼485 and ∼550 nm for As- and Sb-related emissions, respectively. Notably, the implanted impurity concentration is only at the ∼1 × 1019 cm−3 level and localized at a depth of ∼30 nm below the surface. Based on density functional theory calculations, the observed As-related emission arises from a combined effect of valence band edge shifting by As replacing N isoelectronically and an Arsenic interstitial (Asi3+) defect level formation. The Sb-related emission was attributed only to the substitutional Sb in N site (SbN0) related band energy shift, as previously reported for epitaxial incorporation. This work establishes high-temperature ion implantation as a viable technique to enable effective concurrent impurity activation and crystal damage repair, opening pathways for deep-level defect and bandgap engineering in GaN for energy conversion and photonic and quantum applications.

β-Ga2O3 is a highly promising ultrawide bandgap semiconductor material that is poised to transform the high-power electronics field. The manufacturability of device quality β-Ga2O3 epitaxial films at scale is urgently needed. Using a production-ready closed-coupled showerhead MOCVD reactor with in situ reflectance monitoring, this study presents a detailed investigation of the impact of growth parameters on the epitaxial growth of β-Ga2O3 on both (010) and (001) oriented native substrates, as well as on c-plane sapphire substrates with 0°–8° off-axis orientations. By tuning the showerhead–susceptor gap and mapping the other growth parameters, including annealing, nucleation, growth temperature, reactor pressure, and substrate orientation, we achieved state-of-the-art crystal quality, extraordinary wafer-level thickness uniformity of <1% variation for both 2-in. and 4-in. substrates for growth rates as high as 7.2 μm/h. All growth was performed using TMGa and pure O2 as the precursors and N2 as the carrier gas instead of the more widely used argon; no detectable nitrogen and carbon incorporation was observed by secondary ion mass spectrometry. For the homoepitaxy of Si-doped β-Ga2O3 films on (010) substrates, a room temperature Hall mobility of 148 cm2/V s was achieved at a carrier concentration of 1.26 × 1017 cm−3, with a growth rate of 2.6 μm/h. For the heteroepitaxy on sapphire, off-axis substrates exhibited enhanced crystallinity, as shown by the continued reduction of x-ray diffraction rocking curve full width at half maximum from 2834 to 1300 arcsec for 0° and 8° offcut sapphire substrates, respectively. The results demonstrate the scalability and potential advantages of this reactor design for manufacturing-scale β-Ga2O3 growth and offer new insights into the controllability of uniform high-quality films for power electronics applications.

GaN and related semiconductors have become an increasingly prominent material for a wide range of active and passive devices from optoelectronics to high frequency and power electronics as well as photocatalysis. Regardless of the application, anisotropic etching is required for micro and nano structuring, currently performed by reactive ion etching (RIE). Alternately, metal-assisted chemical etching (MacEtch) is an open-circuit plasma-free anisotropic etching method that has demonstrated high aspect ratio device structures devoid of plasma-induced damage found in RIE. This paper presents an in-depth study of the ensemble electrochemical mechanisms that govern the photo-enhanced MacEtch process of GaN and related heterojunctions. Through in-depth experimental investigations, modeling and simulations, the effects of local cathode and anode design, energy-band alignments, and solution chemistry on MacEtch are correlated with the underlying electronic mechanisms of carrier generation, annihilation, transport, and extraction, establishing a fundamental framework for parametrized prediction of system behavior. These findings carry profound implications for tailored design of photoelectrochemical processes employed not just for uniformly etching wide/ultrawide bandgap materials but more broadly for semiconductor-based photocatalytic reactions in general. One-pot photo-enhanced MacEtching of AlInGaN multi-heterojunction device structures including superlattices and multi-quantum wells are demonstrated.

Understanding the thermal stability and degradation mechanism of β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial for their high-power electronics applications. This work examines the high temperature performance of the junctionless lateral β-Ga2O3 FinFET grown on a native β-Ga2O3 substrate, fabricated by metal-assisted chemical etching with Al2O3 gate oxide and Ti/Au gate metal. The thermal exposure effect on threshold voltage (Vth), subthreshold swing (SS), hysteresis, and specific on-resistance (Ron,sp), as a function of temperature up to 298 °C, is measured and analyzed. SS and Ron,sp increased with increasing temperatures, similar to the planar MOSFETs, while a more severe negative shift of Vth was observed for the high aspect-ratio FinFETs here. Despite employing a much thicker epilayer (∼2 μm) for the channel, the high temperature performance of Ion/Ioff ratios and SS of the FinFET in this work remains comparable to that of the planar β-Ga2O3 MOSFETs reported using epilayers ∼10–30× thinner. This work paves the way for further investigation into the stability and promise of β-Ga2O3 FinFETs compared to their planar counterparts.

Human skin contains slowly adaptive (SA) and rapidly adaptive (RA) mechanoreceptors, which respond differently to external stimuli. Based on human tactile perception principles, the fabrication of a self-powered electronic skin (e-skin) that simultaneously mimics SA- and RA-mechanoreceptors is a prime need for robots and artificial prosthetics to interact with the surrounding environment. However, the complex process of merging multimode sensors to mimic SA- and RA-mechanoreceptors hinders their utilization in e-skins. We proposed SA- and RA-mechanoreceptors based on n-type and semi-insulating GaN nanowire arrays. The SA- and RA-mechanoreceptors demonstrated distinguished features such as grasping of objects and detection of their surface textures. Based on piezoelectric sensing principles, the proposed e-skin can simultaneously mimic static and dynamic pressure signals. Mechanoreceptors further detected several stimuli of various pressures with low and high frequencies. The response and reset times showed by SA-mechanoreceptors were 11 and 18 ms under 1-Hz frequency, which are rapid enough for practical e-skin applications.

Rapid development of micro‐electromechanical systems increases the need for flexible and durable piezoelectric nanogenerators (f‐PNG) with high output power density. In this study, a high‐performance, flexible, and highly stable f‐PNG is prepared by directly growing the Mg‐doped semi‐insulating GaN nanowires (NWs) on a 30‐µm‐thick tungsten foil using vapor–liquid–solid growth mechanism. The direct growth of NWs on metal foil extends the overall lifetime of the f‐PNG. The semi‐insulating GaN NWs significantly enhance the piezoelectric performance of the f‐PNG by reducing free electron density. Additionally, the direct integration of NWs on the tungsten foil improves the conductivity, resulting in current enhancement (2.5 mA) with an output power density of 13 mW cm⁻². The piezoelectric performance of the f‐PNG is investigated under several bending angles, actuation frequencies, continuous vibrations, and airflow velocities. The maximum output voltage exhibited by the f‐PNG is 20 V at a bending angle of 155°. The f‐PNG is connected to the backside of an index finger to monitor finger bending behavior by changing the current density. Depending on its flexibility and sensitivity, the f‐PNG can be used as a health‐monitoring sensor to be mounted on joints (fingers, hands, elbows, and knees) to monitor their repeated bending and relaxation.