Molecular Beam Epitaxy Growth of Large‐Area GaN/AlN 2D Hole Gas Heterostructures

Physica Rapid Research Ltrs

Bader

et al. 2021

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Undoped GaN/AlN heterostructures with a high‐density 2D hole gas (2DHG) have recently been reported, demonstrating that holes can be generated in GaN without magnesium (Mg) doping. The presence of the high‐density 2DHG in these GaN/AlN heterostructures is expected to result from huge internal polarization fields. Herein, modulation spectroscopy is applied to analyze the built‐in electric fields in the top GaN layer of molecular beam epitaxy (MBE)‐grown GaN/AlN heterostructures with a buried 2DHG using contactless electroreflectance (CER). Experimentally obtained electric field values are compared with self‐consistent Schrödinger–Poisson energy band calculations of the GaN/AlN structures. This coupled experimental and theoretical analysis determines that the Fermi level at the GaN surface is located at ≈1.9 above the valence band (i.e., roughly in the middle of the bandgap)—for structures with undoped and Mg‐doped GaN. Finally, the comparison of calculated 2DHG concentrations in the structures under study with values determined from Hall effect measurements shows excellent agreement further strengthening the result.

Section: Methodsmentioning

confidence: 97%

Electric Fields and Surface Fermi Level in Undoped GaN/AlN Two‐Dimensional Hole Gas Heterostructures

Janicki

Physica Rapid Research Ltrs

Bader

et al. 2021

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“…The growth rate of 0.42 μm h −1 was controlled by the N-plasma RF power of 400 W. A ≈400 nm thick AlN buffer layer was grown at T sub = 790 °C in metalrich conditions. [44] Impurity blocking layers (IBLs) were incorporated into the AlN buffer layer [27] to minimize the effect of impurities from the substrate on the 2DHG transport and compensation. After the growth of AlN buffer layer, the substrate was cooled down to T sub = 655 °C for the growth of the InGaN layer during an ≈2.…”

Section: Methodsmentioning

confidence: 99%

Very High Density (>10¹⁴ cm⁻²) Polarization‐Induced 2D Hole Gases Observed in Undoped Pseudomorphic InGaN/AlN Heterostructures

Zhang

Xing

et al. 2022

Adv Elect Materials

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High hole densities are desired in p‐channel field effect transistors to improve the speed and on‐currents. Building on the recently discovered undoped, polarization‐induced GaN/AlN 2D hole gas (2DHG), this work demonstrates the tuning of the piezoelectric polarization difference across the heterointerface by introducing indium in the GaN channel. Using careful design and epitaxial growths, these pseudomorphic (In)GaN/AlN heterostructures result in some of the highest carrier densities of >1014 cm−2 in a III‐nitride heterostructure—just an order below the intrinsic crystal limit of ≈1015 cm−2. These ultra‐high density InGaN/AlN 2DHGs show room temperature mobilities of 0.5–4 cm2 V−1 s−1 and do not freeze out at low temperatures. A characteristic alloy fluctuation energy of 1.0 eV for hole scattering in InGaN alloy is proposed based on the experiments.

“…Various groups have demonstrated the growth of AlN buffer layers for HEMTs using MOCVD [33], plasma-assisted (PA) MBE [34], ammonia (NH 3 ) MBE [35]. The AlN layers have been grown on various substrates such as MOCVD-grown AlN on Sapphire templates [36], 6 H-SiC [37] and Bulk single crystal AlN [34] as starting substrates. 6 H-SiC is typically the substrate of choice for highpower RF transistors due to its low lattice mismatch with respect to AlN, high thermal conductivity and availability of large wafers.…”

Section: Growth Of Aln Devicesmentioning

confidence: 99%

Next generation electronics on the ultrawide-bandgap aluminum nitride platform

Hickman

Semicond. Sci. Technol.

Bader

et al. 2021

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Gallium nitride high-electron-mobility transistors (GaN HEMTs) are at a point of rapid growth in defense (radar, SATCOM) and commercial (5G and beyond) industries. This growth also comes at a point at which the standard GaN heterostructures remain unoptimized for maximum performance. For this reason, we propose the shift to the aluminum nitride (AlN) platform. AlN allows for smarter, highly-scaled heterostructure design that will improve the output power and thermal management of III-nitride amplifiers. Beyond improvements over the incumbent amplifier technology, AlN will allow for a level of integration previously unachievable with GaN electronics. State-of-the-art high-current p-channel FETs, mature filter technology, and advanced waveguides, all monolithically integrated with an AlN/GaN/AlN HEMT, is made possible with AlN. It is on this new AlN platform that nitride electronics may maximize their full high-power, high-speed potential for mm-wave communication and high-power logic applications.