Very high channel conductivity in low-defect AlN/GaN high electron mobility transistor structures

Abstract

Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (>1800 cm2/V s) and sheet charge density (>3×1013 cm−2), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to ∼100 Ω/◻ at room temperature. Fabricated 1.2 μm gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ∼1.3 A/mm and a peak transconductance of ∼260 mS/mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented.

Schottky diodes and high electron mobility transistors of 2DEG AlGaN/GaN structures on sapphire substrate

“…It shows almost saturated drain currents reaching more than 320 mA/ mm at U GS = 2 V when normalized to the transistor gate width of 2 × 100 µm. A tiny decline seen in the output characteristics at higher gate voltages is caused by the heating effects which disappears in pulsed I-V characteristics [14]. The pinch-off voltage was measured at around -3.2 V and that was the similar value found from the C-V characteristics of the Schottky diodes (see also Fig.…”

“…The leakage currents dependence on drain voltage was expected after the discussion about the performance of Schottky diodes (see the text above). The HEMT transconductance was found to be more than g m = 100 mS/ mm at used bias of U GS = 0 V and U DS = 6.0 V. The performance of the fabricated 2.5 μm gate length HEMTs was still up to three times worse in comparison to the HEMTs fabricated using more advanced submicron photolithography or nanolithography procedures [10,[14][15]. …”

Effect of residual H 2 O on epitaxial AlN film growth on 4H-SiC by alternating doses of TMA and NH 3

“…There have been many efforts to deposit an epitaxial AlN film using physical vapor deposition (PVD) methods. The conventional way for growing an epitaxial AlN film is molecular beam epitaxy (MBE) [11,12]. In MBE, the aluminum is evaporated (>1200 • C) from a standard effusion cell while nitrogen is decomposed in an electron cyclotron resonance (ECR) plasma.…”

AlN/GaN-Based MOS-HEMT Technology: Processing and Device Results

“…This is required for the following reasons: (1) to obtain the maximum value of drain current, I DSMAX , (2) to reduce the on-resistance, (3) to minimise the power dissipation in the Ohmic contacts because of the high current densities, and (4) to obtain the maximum value of extrinsic transconductance, G MAX , which results in the enhancement of the current gain cutoff frequency, f T , as well as maximum frequency of oscillation, f MAX , of the devices. For these reasons, Ohmic contact optimisation processing for HEMT and MOS-HEMT in the AlN/GaN material systems is crucial to achieving good device performance.…”

“…Key properties of this material system are high 2DEG sheet carrier concentration at the heterojunction interface, high carrier electron velocity, and large electric breakdown field, and so superior performance compared to conventional AlGaN/GaN devices could be achieved. With improvements in material growth and processing techniques, record performances made in this material system include 2DEG sheet carrier concentration over 3 × 10 13 cm −2 with very low sheet resistance, R sh , <150 Ω/£ [1,2], output drain current density over 2 A/mm, transconductance over 400 mS/mm [3,4], and cutoff frequency over 100 GHz [5].…”