Diamond transistors are promising as high-power and high-frequency devices having higher efficiencies than conventional transistors. Diamond possesses superior electronic properties, such as a high bandgap (5.47 eV), high breakdown voltage (>10 MV cm−1 ), high electron and hole mobilities [4500 and 3800 cm2 V−1 · s−1, respectively], high electron and hole saturation velocities (1.5 × 107 and 1.05 × 107 cm s−1, respectively), and high thermal conductivity [22 W cm−1 · K−1], compared to conventional semiconductors. Reportedly, the diamond field-effect transistors (FETs) have shown transition frequencies (fT) of 45 and 70 GHz, maximum oscillation frequency (fmax) of 120 GHz, and radiofrequency (RF) power densities of 2.1 and 3.8 W mm−1 at 1 GHz. A two-dimensional-hole-gas (2DHG) surface channel forms on H-diamond by transfer doping from adsorbates/dielectrics in contact with H-diamond surface. However, prior studies indicate that charge transfer at the dielectric/ H-diamond interface could result in relatively low mobility attributed to interface scattering from the transferred negative charge to acceptor region. H-terminated diamond exhibits a negative electron affinity (NEA) of -1.1 to -1.3 eV, which is crucial to enable charge transfer doping. To overcome these limitations modulation doping, that is, selective doping, that leads to spatial separation of the MoO3 acceptor layer from the hole channel on H-diamond has been proposed. Molybdenum oxide (MoO3) was used as dielectric as it has electron affinity of 5.9eV and could align its conduction band minimum (CBM) below the valence band maximum (VBM) of H-terminated diamond. The band alignment provides the driving potential for charge transfer. Hafnium oxide (HfO2) was used as interfacial layer since it is a high-k oxide insulator (∼25), having large Eg (5.6 eV), high critical breakdown field, and high thermal stability. This study presents photoemission measurements of the electronic band alignments of the MoO3/HfO2/H-diamond layer structure to gain insight into the driving potential for the negative charge transfer and the location of the negative charges near the interface, in the HfO2 layer or in the MoO3 layer. The diamond hole concentration, mobility, and sheet resistance were characterized for MoO3/HfO2/H-Diamond with HfO2 layers of 0, 2 and 4 nm thickness.

This work investigates the impact of wavelength-selective light trapping on photovoltaic efficiency and operating temperature, with a focus on GaAs and Si devices. A nanostructure array is designed to optimize the efficiency of a III-V narrow-band photonic power converter (PPC). Within finite-difference time-domain (FDTD) simulations, a nanotextured GaInP window layer yields a 25× path-length enhancement when integrated with a rear dielectric-metal reflector. Then, nanotexturing of GaInP is experimentally achieved with electron-beam lithography (EBL) and Cl2/Ar plasma etching. Time-resolved photoluminescence (TRPL) measurements show that the GaAs absorber lifetime does not drop due to the nanotexturing process, thus indicating a path to thinner, higher-efficiency PPCs. Next, wavelength-selective light management is examined for enhanced radiative cooling. It is shown that wavelength-selective optimizations of a module’s emissivity can yield 60-65% greater radiative cooling benefits compared to comparative changes across a broader wavelength range. State-of-the-art Si modules that utilize microtextured cover glass are shown to already achieve 99% of the radiative cooling gains that are possible for a photovoltaic device under full sunlight. In contrast, the sub-bandgap reflection (SBR) of Si modules is shown to be far below ideal. The low SBR of modules with textured Si cells (15%-26%) is shown to be the primary reason for their higher operating temperatures than modules with planar GaAs cells (SBR measured at 77%). For textured cells, typical of Si modules, light trapping amplifies parasitic absorption in the encapsulant and the rear mirror, yielding greater heat generation. Optimization of doping and the rear mirror of a Si module could increase the SBR to a maximum of 63%, with further increases available only if parasitic absorption in the encapsulation materials can be reduced. For thin films, increased heat generation may outweigh the photogeneration benefits that are possible with light trapping. These investigations motivate a wavelength-selective application of light trapping: light trapping for near- to above-bandgap photons to increase photogeneration; and out-coupling of light in mid- to far-infrared wavelengths to increase the emission of thermal radiation; but light trapping should ideally be avoided at sub-bandgap energies where there is substantial solar radiation to limit heat generation and material degradation.

The intrinsic material properties of diamond are attractive for use in high power limiter/receiver protector (RP) systems, especially the ones required at the input of radio transceivers. The RP device presents a low capacitance and high resistance to low input signals, thereby adding negligible insertion loss to these desired signals. However, at high input radio frequency (RF) power levels, the RP turns on with a resistance much smaller than the 50 Ω characteristic impedance, reflecting most of the potentially damaging input power away from the receiver input. P-type-intrinsic-n-type (PIN) diodes made of Silicon and Gallium Arsenide used in today’s conventional RP systems have certain limitations at high-power. The wide bandgap of diamond combined with its higher thermal conductivity give it a superior RF power handling capability that can protect sensitive RF front-end components from high power incident signals.

Vertical diamond PIN diodes were proposed and fabricated with an n+-i-p++ structure consisting of: a very thin and heavily phosphorus-doped n-type diamond layer and an intrinsic diamond layer grown on a heavily boron-doped diamond substrate with a (111) crystallographic orientation. Direct current (DC) and RF small-signal characterization was carried out by attaching the diamond sample in a shunted coplanar waveguide (CPW) configuration.

The small-signal lumped element model of the diode impedance under forward-bias was validated with a fit to the measured data, and provides a roadmap for the optimization of parameters for the implementation of diamond Schottky PIN diodes to be successfully used in receiver protector/limiter applications at S-band. The experimental results with the device growth and fabrication show promise and can help in further elevating the device RF figure of merit, in turn enabling the path for commercialization of these diamond-based devices.

This research has studied remote plasma enhanced atomic layer deposited Ga2O3 thin films with gallium acetylacetonate (Ga(acac)3) as Ga precursor and remote inductively coupled oxygen plasma as oxidizer. The Ga2O3 thin films were mainly considered as passivation layers on GaN. Growth conditions including Ga(acac)3 precursor pulse time, O2 plasma pulse time, N2 purge time and deposition temperature were investigated and optimized on phosphorus doped Si (100) wafer to achieve a saturated self-limiting growth. A temperature growth window was observed between 150 ℃ and 320 ℃. Ga precursor molecules can saturate on the substrate surface in 0.6 s in one cycle and the plasma power saturates at 150 W. A growth rate of 0.31 Å/cycle was observed for PEALD Ga2O3. Since the study is devoted towards Ga2O3 working as passivation layer on GaN, the band alignment of Ga2O3 on GaN were further determined with X-ray Photoemission Spectroscopy and Ultraviolet Photoemission Spectroscopy. Two models are often used to decide the band alignment of a heterojunction: the electron affinity model assumes the heterojunction aligns at the vacuum level, and the charge neutrality level model (CNL) which considers the presence of an interface dipole. The conduction band offset (CBO), valence band offset (VBO) and band bending (BB) of PEALD Ga2O3 thin films on GaN were 0.1 ±0.2 eV, 1.0±0.2 eV and 0.3 eV respectively. Type-I band alignments were determined. Further study including using PEALD Ga2O3 as passivation layer on GaN MOS gate and applying atomic layer etching to GaN was described.