Matthew Laurent

Recent progress in metal-organic chemical vapor deposition of

Progress in metal-organic chemical vapor deposition of high quality N-polar (Al, Ga, In)N films on sapphire, silicon carbide and silicon substrates is reviewed with focus on key process components such as utilization of vicinal substrates, conditions ensuring a high surface mobility of species participating in the growth process, and low impurity incorporation. The high quality of the fabricated films enabled the demonstration of N-polar (Al, Ga, In)N based devices with excellent performance for transistor applications. Challenges related to the growth of high quality N-polar InGaN films are also presented.

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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.

N-polar group-III nitrides

Different back barrier designs comprising of AlN, AlGaN, and InAlN layers are investigated for ultra-thin GaN channel N-polar high-electron-mobility-transistors grown by metalorganic chemical vapor deposition. A combinational back barrier with both AlGaN and InAlN materials is proposed. The dependence of channel conductivity on channel thickness is investigated for different back barrier designs. The study demonstrated that the back barrier design of AlN/InAlN/AlGaN is capable of retaining high channel conductivity for ultra-scaled channel thicknesses. For devices with 5-nm-thick channel, a sheet resistance of ∼230 Ω/◻ and mobility ∼1400 cm2/V-s are achieved when measured parallel to the multi-step direction of the epi-surface.

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

This paper reports 400-GHz fmax using a tall-stem T-gate on an N-polar GaN/InAIN MIS-HEMT grown by MOCVD. This is the highest reported fmax value to date for an N-polar GaN HEMT and is among the highest values for all GaN HEMTs. GaN-based HEMTs.

Very high channel conductivity in ultra-thin channel N-polar GaN/(AlN, InAlN, AlGaN) high electron mobility hetero-junctions grown by metalorganic chemical vapor deposition

III-N materials, especially ternary and quaternary alloys, are profoundly affected by barrier height inhomogeneity as evidenced by great variability in reported barrier height and Richardson constant values for Schottky diode samples involving epilayers with identical material composition. Research into AlInGaN-based devices is gaining traction due to its usefulness for strain engineering, polarization engineering, and vertical device design. Thus it is important to characterize the Schottky barrier height between AlInGaN and technologically relevant metals like nickel. It is proposed that alloy composition fluctuations inherent to low-temperature III-N alloys result in a Schottky barrier height inhomogeneity, and that the Schottky barrier height follows a Gaussian distribution. Current vs voltage data as a function of temperature was measured for three AlInGaN samples of varying composition. Utilizing a model tailored to thermionic emission over a Gaussian distribution of barriers, both the average barri...

N-polar GaN/InAlN MIS-HEMT with 400-GHz ƒ max

The design of III–nitride-based hot electron transistors (HETs) is investigated using different diode design methodologies. Barrier-limited forward bias current and low reverse leakage current are demonstrated for the emitter-base diode using a barrier formed by a high-Al% AlGaN layer as a polarization-dipole layer. Two different base-collector diode designs are compared, one using 30% AlGaN as the barrier and the other using 10% InGaN as a polarization-dipole barrier. The InGaN polarization-dipole approach is shown to exhibit much lower reverse leakage currents. The impact of threading dislocation density on diode characteristics is also discussed.

Barrier height inhomogeneity and its impact on (Al,In,Ga)N Schottky diodes

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.

Design of polarization-dipole-induced isotype heterojunction diodes for use in III–N hot electron transistors

Transistor operation by common emitter (CE) current modulation is shown for the first time in III-N hot electron transistors (HETs). The emitter and collector barriers (φ_BE and φ_BC) are implemented using Al_0.45 Ga_0.55N and In_0.1Ga_0.9N layers as polarization dipoles, respectively. CE modulation is achieved by increasing the E-B barrier height beyond the B-C barrier height by increasing the Al_0.45Ga_0.55N thickness (t). Similar CE performance is seen in the identical HET structures grown on both bulk GaN and sapphire. A maximum α of ~0.3 is achieved using a GaN base thickness of 10 nm. The InGaN dipole used as the collector barrier is shown to be instrumental in enabling ohmic base contacts, low base sheet resistance, and low collector leakage, simultaneously.

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

As compared with ternary nitrides systems such as InGaN, AlGaN and InAlN, quaternary (Al,In,Ga)N benefit from a significant increase in design freedom. Indeed changes in the III site atomic fraction allows for an independent choice of either band-gap, lattice constant or polarization which is particularly interesting in the field of solid state lighting, radio frequency (RF), and power electronics. Controlling the homogeneity of the alloy is of great interest to understand the physical properties of (Al,In,Ga)N based devices [1,2]. Atom probe tomography (APT) has demonstrated its ability to evidence alloy fluctuations in ternary nitride [3]. However, detection artifacts in APT could lead to misinterpretation of the actual compositions [4,5]. Calibration experiments are required to find evaporation parameters which enable for an accurate quantification of all III site atoms in (Al,In,Ga)N.

Design Space of III-N Hot Electron Transistors Using AlGaN and InGaN Polarization-Dipole Barriers

The design space of conventional semiconductor devices - from the materials point of view - is currently set by heteroepitaxy, whose capability is strongly limited by lattice parameters and structures of materials of interest. Heterostructures of substantially different semiconductors may offer significant advantages in device design, but many of them are likely heteroepitaxy-incompatible. In such cases, direct wafer-bonding can be exploited, in which materials of interest are separately grown and then their heterostructures formed by thermo-compression. InGaAs, with its superior electron mobility and injection velocity, is considered as the best candidate material for achieving electronic devices in THz applications, whereas III-N has proven its promise in high-power applications. Thus, transistors consisting of InGaAs channel and III-N drain may potentially attain both the high-speed and high-power performances. The first bonded aperture vertical electron transistor (BAVET) with In0.53Ga0.47As channel and Ga-polar InGaN/GaN drain was demonstrated in 2009 [1], and further improvements on it have also been reported [2], [3]. Here, we demonstrate the first BAVET consisting of In0.53Ga0.47As channel and N-polar In0.1Ga0.9N/GaN drain, which has an inherent advantage over Ga-polar InGaN/GaN drain, as discussed below.