[TuB1] Terahertz Devices

9:45 AM - 10:00 AM JST(12:45 AM - 1:00 AM UTC)

[TuB1-05] Etchback emitter metal and dry-etched mesa for InP HBTs

〇Samuel Wachs¹, Nripendra Halder¹, Hady Yacoub¹ (1. Ferdinand-Braun-Institut (Germany))

The emitter mesa of an InP double heterojunction bipolar transistor (DHBT) is typically formed by wet etching, which leads to an undercut along the crystal interfaces. This limits the device performance due to a high base access width for a fixed layer stack and a small active device footprint compared to the contact width. Dry-etching methods such as inductively coupled plasma (ICP) combined with reactive ion etching (RIE) offer an alternative, since the etching process in plasma avoids creating an undercut. We present a process using a combination of dry and wet-etching methods to improve emitter mesa foot to contact head ratio. This leads to a larger effective device area and additionally decreases the base resistance R_b by reducing the base access width. An SiO₂ hard mask is used to protect the TiW/Ti emitter contact structured in an etchback process. The 850 nm node device shows an improved performance with a dc gain β > 30 and a maximum oscillation frequency f_max = 300 GHz.