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.
Large‐area growth of polarization‐induced 2D hole gases (2DHGs) in a GaN/AlN heterostructure using molecular beam epitaxy (MBE) is demonstrated. A study of the effect of metal fluxes and substrate temperature during growth is conducted to optimize the 2DHG transport. These conditions are adopted for the growth on 2 in. wafer substrates. The obtained results represent a step forward towards achieving a GaN/AlN 2DHG platform for high‐performance wide‐bandgap p‐channel field effect transistors (FETs).
- Award ID(s):
- 1719875
- NSF-PAR ID:
- 10130848
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- physica status solidi (b)
- Volume:
- 257
- Issue:
- 4
- ISSN:
- 0370-1972
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Electric Fields and Surface Fermi Level in Undoped GaN/AlN Two‐Dimensional Hole Gas Heterostructuresmore » « less
-
more » « less
The recent demonstration of W mm−1output power at 94 GHz in AlN/GaN/AlN high‐electron‐mobility transistors (HEMTs) has established AlN as a promising platform for millimeter‐wave electronics. The current state‐of‐art AlN HEMTs using ex situ‐deposited silicon nitride (SiN) passivation layers suffer from soft gain compression due to trapping of carriers by surface states. Reducing surface state dispersion in these devices is thus desired to access higher output powers. Herein, a potential solution using a novel in situ crystalline AlN passivation layer is provided. A thick, 30+ nm‐top AlN passivation layer moves the as‐grown surface away from the 2D electron gas (2DEG) channel and reduces its effect on the device. Through a series of metal‐polar AlN/GaN/AlN heterostructure growths, it is found that pseudomorphically strained 15 nm thin GaN channels are crucial to be able to grow thick AlN barriers without cracking. The fabricated recessed‐gate HEMTs on an optimized heterostructure with 50 nm AlN barrier layer and 15 nm GaN channel layer show reduction in dispersion down to compared with in current state‐of‐art ex situ SiN‐passivated HEMTs. These results demonstrate the efficacy of this unique in situ crystalline AlN passivation technique and should unlock higher mm‐wave powers in next‐generation AlN HEMTs.
-
more » « less
Abstract 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.
-
more » « less
Aluminum nitride (AlN) offers novel potential for electronic integration and performance benefits for high‐power, millimeter‐wave amplification. Herein, load‐pull power performance at 30 and 94 GHz for AlN/GaN/AlN high‐electron‐mobility transistors (HEMTs) on silicon carbide (SiC) is reported. When tuned for peak power‐added efficiency (PAE), the reported AlN/GaN/AlN HEMT shows PAE of 25% and 15%, with associated output power () of 2.5 and 1.7 W mm−1, at 30 and 94 GHz, respectively. At 94 GHz, the maximum generated is 2.2 W mm−1, with associated PAE of 13%.
-
more » « less
Abstract 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 >1014cm−2in a III‐nitride heterostructure—just an order below the intrinsic crystal limit of ≈1015cm−2. These ultra‐high density InGaN/AlN 2DHGs show room temperature mobilities of 0.5–4 cm2V−1s−1and 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.
