Al-free InP-based high electron mobility transistors: Design, fabrication and performance

Abstract

We review the design, fabrication and performance of LP-MOVPE grown Al-free InP/In x Ga 1 − x As/InP (53% ≤ x ≤ 81%) high electron mobility transistors (HEMTs) with two types of barrier-enhancement layers; (1) a lattice-matched p +-type doped InP quasi-Schottky barrier layer (junction-modulated HEMT or JHEMT) and (2) a strained undoped In 0.75Ga 0.25P Schottky barrier layer (conventional HEMT). First, the advantages and drawbacks of Al-free InP-HEMTs are summarized from the physical point of view and compared with the conventional InAlAs/InGaAs/InP material system. After a short description of the fabrication process a typical layer structure is shown and the optimum parameters for each layer are deduced with the help of different characterization methods. Thereby, special attention is given to the influence of the In-mole fraction in the InGaAs channel on the DC- and RF-performance of 1 μm gate-length devices. In a later section, the limits concerning the application of JHEMTs in ultra-high speed circuits are discussed and results of devices with L G down to 0.18 μm are shown. As one solution to shortening the gate length without the appearance of negative short channel effects, devices with u-In 0.75Ga 0.25P as barrier-enhancement layer and L G = 0.25 μm are presented. Finally, the RF-performance between GaAs- and InP-based HEMTs and our devices is compared. This comparison demonstrates the excellent potential of Al-free InP-HEMTs for microwave and mm-wave applications.