In-rich InxAl1-xN layers were grown on sapphire substrates with an AlN nucleation layer by metal-organic chemical vapour deposition (MOCVD). Deposition parameters were varied to achieve a high In molar fraction and optimized microstructure without InAlN phase separation. Continuous flow epitaxy (CFE) and, for the first time, flow-modulated epitaxy (FME) MOCVD growth methods were applied to In-rich InAlN. Diverse micro-structural analyses were focused on the study of various crystal defects, including dislocations, significantly inclined grains, voids, and phase separation of different kinds, and were supported by electrical and optical measurements. The best structural quality was obtained by FME in 170 nm thick N-polar In0.64Al0.36N, demonstrating respective screw-and edge-type dislocations densities of 0.61 & times; 109cm-2 and 61 & times; 109cm-2, pits density of 2.4 & times; 108cm-2, surface RMS roughness of 5.3 nm, an electron density and mobility of 1.3 & times; 1019cm-3 and 37.4 cm2/Vs, respectively, and an optical band gap of 1.62 eV.

Apart from providing high-quality ohmic contacts to III-N devices, n(++) GaN cap layers can eliminate surface-related current collapse effects in high-electron-mobility transistors (HEMTs). Various metal-organic chemical vapor deposition conditions and n-type doping are tested in GaN growth on sapphire by using triethylgallium as a Ga precursor, replacing more conventional trimethylgallium. Consequently, despite relatively low temperature of the growth at 800 degrees C to facilitate InAlN barrier capping, optimized growth conditions and SiH4 flow provided free electron concentration of 7.2 x 10(19) cm(-3) and mobility of 103 cm(2)/Vs. Moreover, electron concentration in the range of 10(20) cm(-3) is demonstrated by using flow modulation epitaxy. On the other hand, as calibration growths indicated, excessive SiH4 flow alone can lead to high density of edge dislocations and surface undulations without enhancing free electron concentration. 6 nm (Si: 4.2 x 10(19) cm(-3)) and 8 nm thick (Si: 7.2 x 10(19) cm(-3)) n(++) GaN cap is implemented in normally-off n(++) GaN/InAlN/AlN/GaN HEMTs grown on Si, with a collapse-free performance for the latter case. By calculating energy band and free carrier concentration profiles of the heterostructures it is shown, that free electrons of a sufficiently thick and doped n(++) GaN cap can shield the channel from the unstable surface potential.

N-polar InN/In0.61Al0.39N heterostructures are grown directly on sapphire by using metalorganic chemical vapor deposition. The thickness of Mg-doped In0.61Al0.39N is 340 nm, and the root-mean-square surface roughness of 20 nm thick InN is ∼3.2 nm. An optional AlN spike grown at 710 °C for 35 s is used either as an interlayer to separate the InAlN buffer from the InN channel or as a part of InAlN nucleation after sapphire nitridation. High-resolution transmission electron microscopy reveals approximately two monolayers of AlN if used as the interlayer. In this case, the concentration of screw and edge threading dislocations in partially strained InN decreased down to 6.5 × 109 and 38 × 109 cm−2, respectively. More importantly, the interlayer inclusion suppressed remote donor and alloy disorder scatterings, providing, at room temperature, the InN free electron mobility and concentration of 620 cm2/V s and 3 × 1013 cm−2, respectively. On the other hand, omitting the AlN spike by InAlN nucleation led to structural deteriorations while buffer resistivity increased to 1.7 kΩ/□. A current density of ∼12–16 A/mm, breakdown field of ∼75 kV/cm, and electron drift velocity of ∼2 × 107 cm/s were determined in InN by applying 10 ns voltage pulses on fabricated test resistors.

We present a comprehensive analysis of structural and charge transport properties of high-quality N-polar InN/In0.61Al0.39N heterostructures grown by metalorganic chemical vapour deposition (MOCVD). We observed a strong correlation between the HCl surface treatment and electron mobility. The mobility reduction for structure without AlN nucleation was affected by a thinner native surface oxide formation (supported by the lower I-O/I-N area ratio similar to 0.7), where the surface roughness could play a more significant role.

In0.61Al0.39N layers were doped by Mg using a variable flow of the Cp2Mg precursor at 30 or 80 nmol/min to serve as buffer layers for thin InN layer growth on sapphire substrates by MOCVD. XRD, TEM, SEM, and AFM analyses showed a deterioration of the InAlN structural quality together with phase separation on a nanometer scale with a notable In/Al composition modulation towards the surface of the InAlN layer for the higher Cp2Mg flow. The extracted InN electron mobility also decreased from 471 cm2/Vs for the Cp2Mg flow of 30 nmol/min to 380 cm2/Vs for the Cp2Mg flow of 80 nmol/min.

Herein, vertical GaN transistors with a semi‐insulating (SI) 1.3 μm thick channel layer and C doping of 1 × 10 17 cm −3 are studied. Structures are grown using a metal–organic chemical vapor deposition on conductive GaN substrates. SI GaN is sandwiched between 2.5 μm thick n‐GaN drift layer (Si doping of ≈ 1 × 10 17 cm −3 ) and a top n‐GaN contact layer. A circular mesa region with a diameter of 180 μm is patterned using a deep dry etching. The gate contact formed on the mesa sidewall is insulated from the vertical channel using a 20 nm thick Al 2 O 3 grown by an atomic layer deposition. Despite a robust layout, transistors transfer characteristics indicate normally off behavior if extracted from the linearly scaled current–voltage characteristics and an open channel drain current of 30 mA at the gate bias of 4 V. Achieved on/off ratio is 10 7 at −2 V subthreshold gate bias when the full channel depletion is reached. And, 200 ns long gate pulse characteristics show only a marginal trapping even though no post‐metallization annealing is performed. By comparing experimental results with modeling, mobility of free electrons in the channel is found to be about 45 cm 2 V −1 s −1 .

We present a comprehensive analysis of structural and charge transport properties of high-quality N-polar InN/In0.57Al0.43N heterostructures grown by metalorganic chemical vapour deposition (MOCVD) on on-axis c-plane sapphire substrate and off-axis c-plane sapphire substrate misoriented by 4 degrees toward the a-plane. Instead of a typical GaN template, we included an In-rich InAlN buffer layer to mitigate the lattice mismatch between InN and sapphire. We observed a strong correlation between the structural quality of InN and the electron mobility that was measured in a broad temperature range. Experimental results showed that InN grown at 550 degrees C had a higher density of edge-type dislocations, weaker temperature dependence of electron mobility, and higher electron concentration compared with InN grown at 600 degrees C. Our results suggest that acoustic phonon piezoelectric scattering dominated between 150 and 300 K, while dislocations and interface scattering prevailed from 10 to 150 K. The highest electron mobility of 714 cm(2)/Vs at room temperature was obtained for InN grown at 600 degrees C on the on-axis substrate, which corresponded with the lowest density of edge-type dislocations (2.7 x 1010 cm(-2)) and the best surface morphology with a root-mean-square roughness of 1.4 nm.

Metal organic chemical vapor deposition was used to grow N-polar In0.63Al0.37N on sapphire substrates. P-doping was provided by a precursor flow of Cp2Mg between 0 and 130 nmol/min, reaching a Cp2Mg/III ratio of 8.3 × 10−3. The grain structure of 360 nm thick InAlN was spoiled by pits after introducing a flow of CP2Mg at 30 nmol/min. The surface quality was improved with a flow of 80 nmol/min; however, detrimental deterioration appeared at 130 nmol/min. This correlated with the XRD shape and determined density of dislocations, indicating a phase separation at the highest flow. Degenerated n-type conduction and a free carrier concentration of ~1019 cm−3 were determined in all samples, with a minor compensation observed at a CP2Mg flow of 30 nmol/min. The room temperature (RT) electron mobility of ~40 cm2/Vs of the undoped sample was reduced to ~6 and ~0.3 cm2/Vs with a CP2Mg flow of 30 and 80 nmol/min, respectively. Scattering at ionized acceptor/donor Mg-related levels is suggested. RT photoluminescence showed a red shift of 0.22 eV from the virgin 1.73 eV peak value with Mg doping. Mobility degradation was found to be the main factor by InAlN resistivity determination, which increased by two orders of magnitude, approaching ~0.5 Ωcm, at the highest Cp2Mg flow.

Metal organic chemical vapor deposition is used to grow N-polar In-rich InAlN layers directly on on-and off-axis (misoriented by 4 degrees towards a plane) c-plane sapphire substrates. During the InAlN growth, trimethylaluminum, ammonia, and the total flow was kept at 4.74 mu mol/min, 3 slm and 10 slm, respectively, while trimethylindium (TMIn) flow was selected between 8.42 and 13.48 mu mol/min. All samples were grown at about 706 degrees C however; TMIn flow of 10.95 mu mol/min was also tested at the growth temperature of 686 degrees C. With increasing the TMIn flow, the In molar fraction increased from 0.55 to 0.69, irrespectively of the substrate miscut. For the moderate TMIn flow and In molar fraction of less than 0.63, density of screw and edge dislocations were from 0.3 to 12 X 10(9) cm(-2) and 5 to 7 X 10(10) cm(-2), respectively, while decisively lower densities appeared on on-axis structures. On the other hand, InAlN surface RMS roughness was from 1 to 8 nm favouring the off-axis substrate and low TMIn flow. Structural and surface deterioration appeared with the highest TMIn flow of 13.48 mu mol/min and In molar fraction of 0.69, which hold also for reduced temperature of the growth. Nevertheless, room temperature pho-toluminescence full-width at half maximum less than 270 meV appeared for all samples, with maxima between 1.9 and 1.5 eV. In-rich N-polar InAlN grown on on-axis sapphire can be used as a buffer layer in new types of heterostructure devices.

In(Ga)N epitaxial layers were grown on on-axis and off-axis (0001) sapphire substrates with an about 1100 nm-thick GaN buffer layer stack using organometallic chemical vapor deposition at 600 °C. The In(Ga)N layers consisted of a thin (~10–25 nm) continuous layer of small conical pyramids in which large conical pyramids with an approximate height of 50–80 nm were randomly distributed. The large pyramids were grown above the edge-type dislocations which originated in the GaN buffer; the dislocations did not penetrate the large, isolated pyramids. The large pyramids were well crystallized and relaxed with a small quantity of defects, such as dislocations, preferentially located at the contact zones of adjacent pyramids. The low temperature (6.5 K) photoluminescence spectra showed one clear maximum at 853 meV with a full width at half maximum (FWHM) of 75 meV and 859 meV with a FWHM of 80 meV for the off-axis and on-axis samples, respectively.

Proposal and processing aspects of the proof-of-concept InGaN/AlGaN metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT) with etched gate recess and access regions are addressed. Large negative polarization charge in the MOS gate stack provides the HEMT normally-off operation, while free electrons are populated at access regions after the etching. Self-aligned approach was used for gate stacks preparation.

Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared optoelectronic devices and high speed transistors, however InN growth is much more challenging compared to other III-N semiconductors. In this study we analysed the impact of pre-growth vicinal c-plane sapphire substrate nitridation on the electrical, optical, and strucutral properties of N-polar InN/InAlN heterostructures and the InN crystal habit. While a short cool-down nitridation phase resulted in a high quality InAlN layer and low quality InN layer, it was the opposite for a long cool-down nitridation phase. A trade-off between the electrical and optical properties was observed: the short nitridation cool-down produced InN layers with a higher electron mobility of 629 cm2 V−1 s−1 and low photoluminescence (PL) emission, and the long one resulted in InN with a ∼21% lower electron mobility of 497 cm2 V−1s−1 but strong PL emission. Also, a very different InN crystal habit was observed for either case. The short nitridation cool-down was conducive to the formation of a continuous layer consisting mostly of coalesced downward-pointing hexagonal pyramids, while the long one led to a layer of upward-pointing hexagonal pyramids. The local decomposition of an AlON layer produced by sapphire nitridation and variations in the InAlN surface morphology resulting in a preferential attraction of growth species and localised change in the surface free energy contributions were most likely responsible for these observations. Our results also suggest N-polar buffer layers are likely to produce coalesced InN layers with a high electron mobility, while metal-polar buffer layers may facilitate the growth of high crystal quality pyramidal InN with a strong optical response.

Vertical current conduction in a 1.3-mu m-thick semi-insulating ( SI) C-dopedGaN grown on a GaN substrate is analyzed. During the growth, pressure was varied from 100 to 20 mbar in order to increase C concentration from similar to 1 x 10(17) cm(-3) to similar to 6 x 10(18) cm(-3); SI GaN is sandwiched between two n-GaN layers. Optical transitions suggest two acceptor levels: similar to 0.9 eV above the valence band and similar to 0.6 eV below the conduction band. Currentvoltage characterizations reveal a space-charge-limitedcurrent conduction with an impact-ionization-assisted filling of traps in a moderately C-doped sample. On the other hand, highly compensated SI GaN forms a similar to 0.5-eV potential barrier at the interface with n-GaN, whereas the breakdown voltage exceeds 350 V. As the model explains, deep acceptors above the valence band compensate residual donors and lead to an electron mobility collapse. On the other hand, dependingonCconcentration, acceptors below the conduction band play a different role. In the moderately doped SI GaN, they act as electron traps and define the breakdown voltage. On the other hand, acceptors below the conduction band in highly compensated SI GaN are responsible for the barrier-controlled conduction and reaching of the avalanche.

Further progress of information technologies is hampered by the limited operational speed and frequency of contemporary electronic devices. Consequently, there is an intense quest for materials with the highest electron velocity. Over a decade, InN has been predicted to be among the top candidates. However, due to technological constrains of InN growth, this theoretical prediction has not been validated yet. In the present paper, we demonstrate state-of-the-art InN materials with an electron drift velocity of about 1 × 108 cm s−1 at an electric field of 48 kV cm−1. This is the highest steady-state electron velocity ever measured in any solid-state device. Moreover, our experimental value outperforms theoretical predictions by a factor of two, suggesting a need for revised understanding of InN fundamental properties. Moreover, the extracted InN electron velocity is about two times higher compared to the main competitors, such as InAs or graphene, introducing InN as the best far-reaching candidate for the next-generation ultra-fast electronics. We propose that implementation of InN-channel transistors may provide switching speeds deeply in the THz frequency range. If this technology is fully developed, it will help to erase the current THz frequency gap between the electronic and optical devices.

g5rt Samples comprising 1.3 mu m-thick C-doped semi-insulating (SI) GaN layer sandwiched between two n-GaN layers were grown on sapphire or conductive GaN substrates by metal-organic chemical vapor phase epitaxy at varied reactor pressure between 100 and 20 mbar. Vertical cylindrical resistors with a radius of 50 mu m were defined by similar to 1.6 mu m-deep mesa etching down to the bottom Si-doped n-GaN layer. X-ray diffraction rocking curves revealed almost invariant crystallographic quality of homo-epitaxial structures grown on the GaN substrate, while dislocations in GaN on sapphire lead to curve broadening and pits formations. C concentration in SI GaN grown on the GaN substrate was found to increase from similar to 1. 10(17) cm(-3) to similar to 6 x 10(18) cm(-3)as the growth pressure decreased from 100 mbar to 20 mbar. However, one order of magnitude lower C concentration and inhomogeneous distribution was found for the sapphire substrate. I-V characterization showed that the electrical strength of SI GaN could be as high as 2.8 MV/cm if grown at 20 mbar on the GaN substrate. In this case the nondestructive break-down voltage exceeds 350 V with a positive T coefficient pointing on impact ionization. Sample grown on the GaN substrate at 20 mbar demonstrated ln(I) similar to V dependence which is typical for a barriercontrolled leakage. Extracted barrier height of 0.41 eV at the n-GaN/SI GaN interface was explained by C-related compensation effect and by a shifting of the Fermi level. On the other hand, apart from SI GaN grown on GaN substrate at 20 mbar, all other structures showed I = f(V-n) dependence indicating a space-charge-limited current conduction mechanism. It is suggested that the optimized SI GaN grown on GaN substrate can be considered as a current blocking layer or as a channel in robust geometry vertical transistors.

Thick InAlN layers (In-molar fraction >0.37) on GaN buffer layers were prepared using a close-coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor.

InN is a promising III-nitride material for high-speed electronics and for optoelectronic applications in the infrared. We focused on the MOCVD growth of InN films and InAlN buffer layers with InN content in the alloy $x_{\mathrm{I}n} \cong 0.55$ on sapphire substrate. The InN layers were about 100 nm thick and their structural, morphological, and optical properties were evaluated. Surface morphology and crystallinity of the InAlN buffer layer strongly affects the top InN film. The InAlN layer itself was markedly influenced by the preceding nitridation procedure. A decent quality of InN crystal was indicated by the PL peak at about 720 meV with a FWHM of 116 meV at room temperature. We correlated photoluminescence and XRD characteristics of the layers with their morphology. The results underline the importance of the nitridation procedure in the In(Al)N growth.

Polarization engineering is a promising approach to achieve high positive threshold voltage (Vth) in GaN-based metal-oxide-semiconductor high electron mobility transistors (MOS HEMTs). In this paper, we investigate all critical interfaces of polarization-engineered normally-off Al2O3/InGaN/AlGaN/GaN MOS HEMTs using transmission electron microscopy and X-ray photoelectron spectroscopy. Mechanisms of threshold voltage (VTH) instabilities are also analyzed. Devices were subjected to positive-bias stress-recovery experiments to capture the transient change in Vth. We propose a model that explains observed peculiar behavior and discuss the role of 2-dimensional hole gas (2DHG) in Al2O3/InGaN/AlGaN/GaN MOS HEMTs Vth shift.

N‐polar InN/InAlN heterostructure growth and performance are studied on‐ and off‐axis sapphire substrates misoriented toward the m or a plane by 4°. A high In molar fraction (0.57) in the InAlN layer is chosen to reduce the lattice mismatch. InN growth on the on‐axis InAlN/sapphire system is initiated with random island formation, which coalesce at ≈10 nm thickness smearing grain boundaries. In contrast, on off‐axis sapphires, growth is defined by misorientation‐induced steps and grains remain visible even after the layer coalesces. The best electron mobility of 720 cm2 V−1 s−1 and carrier density of ≈1.5 × 1019 cm−3 are demonstrated on the heterostructure grown on‐axis sapphire, with InN as thin as 20 nm, even though the InN/InAlN interface root mean square roughness is ≈1.3 nm. The concentrations of screw and edge dislocations in the 20 nm thick InN grown on the on‐axis system are extracted to be 4.7 × 109 and 3.5 × 1010 cm−2. In all cases, the InN lattice is still partially strained, performing only ≈85% relaxation. Further lowering of the lattice mismatch, smoothing of the InAlN surface, and achieving semi‐insulating InAlN will provide necessary development steps toward predicted InN‐channel transistors with unprecedented performance.