Steven Wienecke

In-situ metalorganic chemical vapor deposition and capacitance-voltage characterizations of Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors

The in-situ metalorganic chemical vapor deposition of Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors (MOSCAPs) is reported. Al2O3 is grown using trimethylaluminum and O2 in the same reactor as GaN without breaking the vacuum. The in-situ MOSCAPs are subjected to a series of capacitance-voltage measurements combined with stress and ultraviolet-assisted techniques, and the results are discussed based on the presence of near-interface states with relatively fast and slow electron emission characteristics. The in-situ MOSCAPs with Al2O3 grown at 900 and 1000 °C exhibit very small hystereses and charge trappings as well as average near-interface state densities on the order of 1012 cm−2eV−1.

Elimination of columnar microstructure in N-face InAlN, lattice-matched to GaN, grown by plasma-assisted molecular beam epitaxy in the N-rich regime

The microstructure of N-face InAlN layers, lattice-matched to GaN, was investigated by scanning transmission electron microscopy and atom probe tomography. These layers were grown by plasma-assisted molecular beam epitaxy (PAMBE) in the N-rich regime. Microstructural analysis shows an absence of the lateral composition modulation that was previously observed in InAlN films grown by PAMBE. A room temperature two-dimensional electron gas (2DEG) mobility of 1100 cm2/V s and 2DEG sheet charge density of 1.9 × 1013 cm−2 was measured for N-face GaN/AlN/GaN/InAlN high-electron-mobility transistors with lattice-matched InAlN back barriers.

N-Polar GaN MIS-HEMTs on Sapphire With High Combination of Power Gain Cutoff Frequency and Three-Terminal Breakdown Voltage

Nitrogen polar SiN_x/AlGaN/GaN/AlGaN metal- insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with 28.6-nm equivalent GaN channel thickness grown by metal-organic chemical vapor deposition on sapphire substrate with a high combination of current/power gain cutoff frequencies (f_T/f_max) and three-terminal breakdown voltage (BV_DS) are demonstrated. f_T/BV_DS of 103 GHz/114 V and f_max/BV_DS of 248 GHz/114 V were achieved in devices with the gate widths of 2 × 50 μm and 2 × 25 μm, respectively, comparing well with recent reports of fully passivated and vertically scaled Ga-polar GaN HEMTs. Devices with a gate width of 2 × 75 μm showed the peak output power densities of 5.74 W/mm at 4 GHz and 6.29 W/mm at 10 GHz obtained by load-pull measurements.

N-Polar GaN Cap MISHEMT With Record Power Density Exceeding 6.5 W/mm at 94 GHz

A novel N-Polar GaN cap (MIS)high electron mobility transistor demonstrating record 6.7-W/mm power density with an associated power-added efficiency of 14.4% at 94 GHz is presented. This state-of-the-art power performance is enabled by utilizing the inherent polarization fields of N-Polar GaN in combination with a 47.5-nm in situ GaN cap layer to simultaneously mitigate dispersion and improve access region conductivity. These excellent results build upon past work through the use of optimized device dimensions and a transition from a sapphire to a substrate for reduced self-heating.

N-Polar Deep Recess MISHEMTs With Record 2.9 W/mm at 94 GHz

W-band power performance is reported on an N-polar GaN HEMT for the first time, resulting in a record output power density for any GaN device on a sapphire substrate. This result is achieved using an N-polar GaN deep recess MISHEMT structure grown by metal-organic chemical vapor deposition on the sapphire substrates. The key component in this device design is the addition of an in situ unintentionally doped GaN epitaxial passivation layer in the access regions of the transistor. This GaN layer functions both to control DC-to-RF dispersion as well as to increase the conductivity in the access regions of the HEMT. Devices with very low dispersion and a simultaneous fmax/ft combination of 276/149 GHz are demonstrated. Load pull measurements at 94 GHz give a peak power added efficiency (PAE) of 20% with an associated output power density of 1.73 W/mm at VDS = 8 V. A record 2.9-W/mm maximum output power density with an associated 15.5% PAE at VDS = 10 V is achieved despite the low thermal conductivity of the samples sapphire substrate.

Small-signal model extraction of mm-wave N-polar GaN MISHEMT exhibiting record performance: Analysis of gain and validation by 94 GHz loadpull

In this paper we extract a small-signal model of a mm-wave deep-recess N-polar GaN MISHEMT exhibiting record 94 GHz power density. We show that certain existing methods for extrinsic parasitic extraction cannot be easily employed because of the device design but that an existing cold-bias method provides accurate extraction. The small-signal model with pad layout parasitics is then validated with the gain measured at low input powers by a 94 GHz loadpull system. The factors impacting the measured gain are analyzed to show their origins and relative impact, giving guidance and predictions for future improvement.

In situ metalorganic chemical vapor deposition of Al2O3 on N-face GaN and evidence of polarity induced fixed charge

The in situ metalorganic chemical vapor deposition (MOCVD) of Al2O3 dielectrics on N-face GaN is reported. The near-interface fixed charges are measured by using capacitance-voltage techniques on a metal-oxide-semiconductor (MOSCAP) structure, and the results are compared with those obtained on Ga-face MOSCAPs with the same in situ MOCVD Al2O3 dielectrics. The influence of GaN polarity as well as other possible mechanisms on the formation of fixed charge are identified and discussed.

W-band passive load pull system for on-wafer characterization of high power density N-polar GaN devices based on output match and drive power requirements vs. gate width

A W-band on-wafer passive load pull system constructed for the characterization of high power density N-polar GaN devices is presented. N-Polar GaNs large RF voltage swing enables high power densities but also increases the power match impedance which must be synthesized with the limited on-wafer tuning range. Increasing test cell gate width to decrease impedance increases the systems drive power requirement. The tradeoff between these is analyzed, showing that a passive load pull system can characterize a wide range of devices. This is demonstrated with measured data from an N-polar GaN device exhibiting 4.1 W/mm power density at 94 GHz.

Extraction of net interfacial polarization charge from Al0.54In0.12Ga0.34N/GaN high electron mobility transistors grown by metalorganic chemical vapor deposition

AlxInyGa(1-x-y)N materials show promise for use in GaN-based heterojunction devices. The growth of these materials has developed to the point where they are beginning to see implementation in high electron mobility transistors (HEMTs) and light emitting diodes. However, the electrical properties of these materials are still poorly understood, especially as related to the net polarization charge at the AlInGaN/GaN interface (Qπ(net)). All theoretical calculations of Qπ(net) share the same weakness: dependence upon polarization bowing parameters, which describe the deviation in Qπ(net) from Vegards law. In this study, direct analysis of Qπ(net) for Al0.54In0.12Ga0.34N/GaN HEMTs is reported as extracted from C-V, I-V, and Hall measurements performed on samples grown by metalorganic chemical vapor deposition. An average value for Qπ(net) is calculated to be 2.015 × 10−6 C/cm2, with just 6.5% variation between measurement techniques.

mm-Wave N-polar GaN MISHEMT with a self-aligned recessed gate exhibiting record 4.2 W/mm at 94 GHz on Sapphire

GaN based high electron mobility transistors have emerged as a leading technology for mm-wave solid state power amplification at W-band. To date, reports on W-band GaN HEMTs and MMICs have primarily featured devices grown in the Ga-polar orientation [1, 2]. In this work, the advantages of the N-polar orientation are exploited to produce a MISHEMT exhibiting record high 4.2 W/mm peak output power (Pout) at 94 GHz. The key enabling advantage of N-polar GaN devices are their inverted polarization fields. These fields create a natural, charge-inducing back-barrier that decouples the tradeoff between aspect ratio and channel electron density. Further, the reversed field in an AlGaN cap above the GaN channel opposes gate leakage and improves breakdown voltage [3]. Additionally, to mitigate surface-state induced dispersion and enhance the conductivity of the access regions, a GaN cap layer is added in the access regions through which the gate is recessed [4]. The fabrication process reported in this paper extends that of [4, 5] to have the foot gate metal deposited in a self-aligned fashion to the GaN cap recess etch.