Epitaxial high-K AlBN barrier GaN HEMTs

Abstract

We report a polarization-induced 2D electron gas (2DEG) at an epitaxial AlBN/GaN heterojunction grown on a SiC substrate. Using this 2DEG in a long conducting channel, we realize ultra-thin barrier AlBN/GaN high electron mobility transistors that exhibit current densities of more than 0.25 A/mm, clean current saturation, a low pinch-off voltage of -0.43 V, and a peak transconductance of 0.14 S/mm. Transistor performance in this preliminary realization is limited by the contact resistance. Capacitance-voltage measurements reveal that introducing 7 % B in the epitaxial AlBN barrier on GaN boosts the relative dielectric constant of AlBN to 16, higher than the AlN dielectric constant of 9. Epitaxial high-K barrier AlBN/GaN HEMTs can thus extend performance beyond the capabilities of current GaN transistors.

Figures (5)

• Figure 1: (a) Epitaxial AlBN/GaN heterostructure indicating a polarization-induced 2DEG at the heterojunction, (b) AFM micrograph, (c) RHEED pattern along [11-20] zone axis, (d) HRTEM micrograph of AlBN/GaN heterostructure. Inset shows FFT analysis of red marked region indicating wurtzite phase. (e) Composition-depth profiles of Al, Ga, $^{11}$B, and $^{10}$B species as measured by ToF-SIMS.
• Figure 2: Temperature-dependent Hall effect measurement data showing electron density, mobility, and sheet resistance from 320 K to 10 K confirming 2DEG properties in the AlBN/GaN heterostructure. The measurement was performed with indium dots on the center 1 cm $\times$ 1 cm sample diced from the 3-inch diameter wafer.
• Figure 3: (a) The device process flow of group III-Nitride HEMTs with alloyed contacts, (b) Schematic cross-section of $\sim$7% B containing AlBN barrier GaN HEMT showing the alloyed contacts, gate, and channel regions. (c) Scanning electron microscope (SEM) image of a processed HEMT showing source (S), drain (D), and gate (G) regions. (d) Room temperature Hall-effect data for $\sim$7% B containing AlBN barrier GaN HEMT measured after device processing.
• Figure 4: (a) Measured characteristics of the GaN HEMT with AlBN barrier with $\sim$7% B: (a) log scale, and (b) and linear scale Transfer characteristics showing an on/off ratio exceeding three orders and Transconductance vs. $V_{\rm gs}$ showing a peak transconductance of 139 mS/mm and. (d) Output characteristics showing on resistance $R_{\rm on}= 6.8$$\Omega$.mm with repeatable current saturation and a maximum drain current $I_{\rm d}$ of 280 mA/mm at a gate voltage $V_{\rm gs}=1.5$ V.
• Figure 5: Measured CV characteristics (points) of 2-nm GaN cap/2.2-nm AlBN/GaN-based metal-insulator-semiconductor (MIS) capacitor at 2 MHz, 20 $^\circ$C overlaid with 1D Schrödinger Poisson simulated CV characteristics indicating the dielectric constant of the AlBN barrier is $\epsilon_{\rm r}^{\rm AlBN} \sim$16.