JunShuai Xue

Pulsed metal organic chemical vapor deposition of nearly latticed-matched InAlN/GaN/InAlN/GaN double-channel high electron mobility transistors

High quality, nearly lattice-matched InAlN/GaN/InAlN/GaN double-channel heterostructures were grown on sapphire by pulsed-metal-organic-chemical-vapor-deposition (PMOCVD). High electron mobility of 1414 cm2/Vs was achieved along with a two-dimensional-electron-gas density of 2.55 × 1013 cm−2. We attribute it to the high quality PMOCVD-grown InAlN barriers and, additionally, to the novel GaN layer growth between two InAlN barriers, which consists of a thin GaN spacer to prevent indium-redistribution and indium-cluster formation during the subsequent growth and a relatively thick GaN channel to enhance electron mobility. High-electron-mobility-transistors fabricated on these heterostructures with 0.8-μm-length gate exhibit a maximum drain current of 906 mA/mm and a transconductance of 186 mS/mm.

Nearly lattice-matched InAlN/GaN high electron mobility transistors grown on SiC substrate by pulsed metal organic chemical vapor deposition

We report on a growth of nearly lattice-matched InAlN/GaN heterostructures on 4H–SiC substrates by pulsed metal organic chemical vapor deposition, and an excellent device characteristic of high electron mobility transistors (HEMTs) fabricated on these InAlN/GaN heterostructures. The electron mobility is 1032 cm2/V s together with a high two-dimensional-electron-gas density of 1.59×1013 cm−2 for the In0.17Al0.83N/AlN heterostructures. HEMTs with gate dimensions of 0.5×50 μm2 and 3 μm source-drain distance exhibits a maximum drain current of 1 A/mm, a maximum extrinsic transconductance of 310 mS/mm, and current gain and maximum oscillation cutoff frequencies of 18 GHz and 39 GHz, respectively.

Trap states in InAlN/AlN/GaN-based double-channel high electron mobility transistors

We present a detailed analysis of trap states in InAlN/AlN/GaN double-channel high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. By frequency dependent conductance measurements, trap densities and time constants at both InAlN/AlN/GaN interfaces were determined. Two types of traps, with a high density of up to ∼1014 cm−2 eV−1, were observed existing at the higher InAlN/AlN/GaN interface. On the other hand, the density dramatically decreased to ∼1012 cm−2 eV−1 for traps located at lower InAlN/AlN/GaN interface on which a low-temperature grown GaN (LT-GaN) layer was deposited. Additionally, photo-assisted capacitance-voltage measurements were performed to estimate deep-level defects, yielding a low density of 1.79 × 1011 cm−2 acting as negative fixed charges at the LT-GaN and lower InAlN interface.

Transport characteristics of AlGaN/GaN/AlGaN double heterostructures with high electron mobility

The AlGaN/GaN/AlGaN double heterostructure (DH) with high electron mobility of 1862 cm2/Vs at room temperature and 478 cm2/Vs at 573 K high temperature was obtained by a combination of optimization schemes considering scattering mechanisms. First, a composite buffer layer structure, including GaN and AlGaN layer, was used to improve the crystal quality of the AlGaN/GaN/AlGaN DH. Second, interface roughness scattering was reduced by increasing the channel thickness, thus the two-dimensional electron gas mobility was further improved. Moreover, an ultrathin AlN interlayer was inserted between the GaN channel layer and the AlGaN buffer layer to decrease the alloy disorder scattering. The Hall effect measurements showed that the DH had better transport characteristics at high temperatures, and an electron mobility of 478 cm2/Vs was achieved at 573 K, which is twice larger than that of the conventional single heterostructure (∼200 cm2/Vs at 573 K). Therefore, AlGaN/GaN/AlGaN DH is more suitable for the applica...

Fabrication and characterization of InAlN/GaN-based double-channel high electron mobility transistors for electronic applications

In our previous work [J. S. Xue et al., Appl. Phys. Lett. 100, 013507 (2012)], superior electron-transport properties are obtained in InAlN/GaN/InAlN/GaN double-channel (DC) heterostructures grown by pulsed metal organic chemical vapor deposition (PMOCVD). In this paper, we present a detailed fabrication and systematic characterization of high electron mobility transistors (HEMTs) fabricated on these heterostructures. The device exhibits distinct DC behavior concerning with both static-output and small-signal performance, demonstrating an improved maximum drain current density of 1059 mA/mm and an enhanced transconductance of 223 mS/mm. Such enhancement of device performance is attributed to the achieved low Ohmic contact resistance as low as 0.33 ± 0.05 Ω·mm. Moreover, very low gate diode reverse leakage current is observed due to the high quality of InAlN barrier layer deposited by PMOCVD. A current gain frequency of 10 GHz and a maximum oscillation frequency 21 GHz are also observed, which are comparab...

Enhancement-mode Al2O3/InAlN/AlN/GaN metal?insulator?semiconductor high-electron-mobility transistor with enhanced breakdown voltage using fluoride-based plasma treatment

We demonstrate an enhancement-mode (E-mode) Al2O3/InAlN/AlN/GaN metal?insulator?semiconductor high-electron-mobility transistor (MISHEMT) with enhanced breakdown voltage. The threshold voltage Vth shifts from ?7.6 to 1.8 V using fluoride-based plasma treatment. The gate leakage current and the buffer leakage current were reduced by the conduction band modulation of negative fluorine charges. The reduction in the buffer leakage current enhanced the breakdown voltage from 80 to 183 V with LGD = 3 ?m. The fabricated E-mode MISHEMT with a gate length of 1 ?m exhibits a respectable drain current of 416 mA/mm and a peak transconductance of 150 mS/mm.

Threading dislocation reduction in transit region of GaN terahertz Gunn diodes

An effect of the position of notch-doping layer in 1-μm GaN Gunn diode on threading dislocations (TDs) distribution is investigated by transmission electron microscopy. Compared with the top-notching-layer (TNL) structure, the bottom-notching-layer (BNL) structure can efficiently reduce the TDs density and improve the crystal quality in the transit region of GaN Gunn diode because it exhibits twice-transition of growth mode from atomic step flow to layer-by-layer nucleation and leads to a significant annihilation of TDs before penetrating into the transit region. X-ray diffraction and Raman spectroscopy reveal that the BNL structure has less compressive stress than the TNL structure.

Interaction between Si doping and the polarization-induced internal electric field in the AlGaN/GaN superlattice

AlGaN/GaN superlattices (SLs) with and without Si doping exhibit very different properties. Because of the difference between the dielectric constants of AlGaN and GaN, the wells of the SL are depleted in the undoped structure. With increased Si doping in the GaN wells, the depletion effect will vanish, and the accumulation of electrons will compensate for the polarization-induced internal electric field (PIIEF) in the AlGaN barrier, which is followed by disturbance of the PIIEF in the GaN wells due to electron overflow from the ground state E0 to the first excited state E1. This leads to a decrease in E1-E0.

Trap state analysis in AlGaN/GaN/AlGaN double heterostructure high electron mobility transistors at high temperatures

In this work, frequency-dependent capacitances and conductance measurements are adopted to investigate high temperature characteristics of trap states in AlGaN/GaN/AlGaN double heterostructure high electron mobility transistors (DH-HEMTs). It is found that fast and slow trap states are present in DH-HEMTs, while only fast traps exist in AlGaN/GaN single heterostructure (SH) HEMTs. In the former, the fast trap state density ranges from 4.6 × 1012 cm−2 eV−1 to 1.9 × 1013 cm−2 eV−1 located at an energy below the conduction band between 0.273 eV and 0.277 eV, and the slow deep trap state density decreases from 2.4 × 1013 cm−2 eV−1 to 8.7 × 1012 cm−2 eV−1 located at an energy ranging from 0.384 eV to 0.423 eV in DH-HEMTs with a 14 nm GaN channel layer. These active trap energy levels in DH-HEMTs become deeper as the thickness of the channel layer decreases. In addition, the active trap energy levels in SH- and DH-HEMTs gradually become deeper as the measurement temperature increases. Also, the change in amplit...

Demonstration of InAlN/AlGaN high electron mobility transistors with an enhanced breakdown voltage by pulsed metal organic chemical vapor deposition

In this work, InAlN/AlGaN heterostructures employing wider bandgap AlGaN instead of conventional GaN channel were grown on sapphire substrate by pulsed metal organic chemical vapor deposition, where the nominal Al composition in InAlN barrier and AlGaN channel were chosen to be 83% and 5%, respectively, to achieve close lattice-matched condition. An electron mobility of 511 cm2/V s along with a sheet carrier density of 1.88 × 1013 cm−2 were revealed in the prepared heterostructures, both of which were lower compared with lattice-matched InAlN/GaN due to increased intrinsic alloy disorder scattering resulting from AlGaN channel and compressively piezoelectric polarization in barrier, respectively. While the high electron mobility transistor (HEMT) processed on these structures not only exhibited a sufficiently high drain output current density of 854 mA/mm but also demonstrated a significantly enhanced breakdown voltage of 87 V, which is twice higher than that of reported InAlN/GaN HEMT with the same devic...