This study proposes an InAlAsSb/InP heterostructure field-effect transistor ͑HFET͒ grown by a low-pressure metallorganic chemical vapor deposition system. Its InAlAsSb Schottky layer and coupled ␦-doped InP channels cause this HFET to exhibit high two-and three-terminal breakdown voltages. Mobility and two-dimensional electron gas concentration are increased. Additionally, this HFET does not exhibit the frequently observed parallel conduction and bell-shaped characteristics of conventional HFETs. The activation energy is also determined.InP-based heterostructures are extremely attractive for a variety of microwave and optoelectronic applications. 1,2 In particular, InAlAs/InGaAs high-electron mobility transistors ͑HEMTs͒ have exhibited enhanced high-speed and low-noise performance because of their superior electronic transport properties, such as high electron mobilities, high electron velocities, and large ⌫ and L valley energy separation. 3 However, the so-called parallel conduction exists in the high bandgap donor layers of HEMTs. The conducting electrons transfer into high bandgap donor layers under the high current operation, resulting in an additional conducting channel. Because of the low electron mobility in the parallel-channel, the realspace transfer of electrons degrades the device performance. Additionally, the high output conductance and low breakdown voltages of HEMTs limit the use of these devices in high-power microwave applications. Although several approaches have been used to enhance the breakdown in HEMTs, the improvements have been limited. Accordingly, an alternative device technology is required to make further improvements. In 1980, Wood et al. proposed planar doping to improve the doping profile abruptness of Gedoped n-type GaAs grown by molecular-beam epitaxy. 4 The single ␦-doped GaAs field-effect transistor ͑FET͒ has numerous advantages, such as high breakdown voltage and easy control of threshold voltages. 5 Zheng et al. demonstrated the enhanced mobility in coupled ␦-doped layers. 6 However, most work on the ␦-doping technique has been focused on the GaAs and AlGaAs systems. 7-9 An excellent alternative material system is lattice-matched In 0.34 Al 0.66 As 0.85 Sb 0.15 /InP, which has a large bandgap ͑ϳ1.8 eV͒, 10 In 0.34 Al 0.66 As 0.85 Sb 0.15 with a high Schottky barrier ͑ B Ͼ 0.73 eV͒, and a large ⌬E C ͑Ͼ0.7 eV͒ at the InAlAsSb/InP heterojunction. 11-13 InP is an attractive material for use in highfrequency power FETs because it has a high electron peak velocity, a low ionization coefficient, and good thermal conductivity. The coupled ␦-doped InAlAsSb/InP heterostructure field-effect transistors ͑HFETs͒ have been demonstrated to exhibit the high mobility and breakdown characteristics. 14,15 However, the breakdown mechanism and temperature-dependent characteristics of the InAlAsSb/InP HFETs have been neglected. This work proposes an InP-based HFET with coupled ␦-doped InP channels and an In 0.34 Al 0.66 As 0.85 Sb 0.15 Schottky layer. This HFET exhibits high mobility, high two-dim...
