Abstract
The capacitance and the series resistance are two main factors which determine the cut-off frequency of Schottky barrier diodes (SBDs) for their application in millimeter-wave and terahertz regions. The junction capacitance is closely related to the anode dimension of a SBD. Reducing the anode size can effectively decrease the junction capacitance, but it will increase the series resistance and the difficulty of the device manufacturing process is also increased. In this paper, an AlGaN/GaN based air-bridge structure planar SBD with a half through-hole is investigated. The half through-hole was formed on the center of a circular anode by inductively coupled plasma etching to the unintentional doping-GaN channel layer. The capacitance formed by the anode metal and the two-dimensional electron gas at the AlGaN/GaN interface is effectively reduced under the condition of holding the metal area of anode. The total capacitance of the 20 μm-radius anode SBD with a 19.95 μm-radius half through-hole dramatically decreases from 2.32 pF of the device without the half through-hole to 21.5 fF. In addition, since the current is mainly distributed at the edge of the circular anode, the series resistance is only slightly increased. The cut-off frequency of the air-bridge planar SBD with a 20 μm-radius anode and a 19.95 μm-radius half through-hole was 114.1 GHz. To reduce the size of the anode and optimize the ohmic contact, the cut-off frequency could be further improved.
Highlights
Terahertz waves (0.1–10 THz), which span the gap between light and radio waves, have a lot of applications in sub-millimeter waves, terahertz wireless communication, synthetic aperture radars, satellite remote sensing, etc
The leakage current mechanism of the Schottky barrier diodes (SBDs) with/without the half through-hole structure was of the trap assistant tunneling (TAT) model when the 2-DEG underlying the Schottky metal was fully depleted under the reverse bias
The junction capacitance formed by the anode metal and 2DEG at the AlGaN/GaN interface is effectively reduced under the condition of holding the metal area of anode
Summary
Terahertz waves (0.1–10 THz), which span the gap between light and radio waves, have a lot of applications in sub-millimeter waves, terahertz wireless communication, synthetic aperture radars, satellite remote sensing, etc. Low capacitance AlGaN/GaN based air-bridge structure planar Schottky diode with a half through-hole AlGaN/GaN based air-bridge structure planar SBDs with a half through-hole are fabricated.
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