A DLTS study of Pt/Al₂O₃/In_xGa_{1 - x}As Capacitors

Abstract

Deep Level Transient Spectroscopy (DLTS) has been applied to MOS capacitors (MOSCAPs) fabricated on n- and p-type GaAs and on n-type InxGa1-xAs epitaxial layers deposited by MBE on GaAs substrates. The gate dielectric consists of 10 nm ALD Al2O3. It is shown that the dominant deep levels in the case of GaAs MOSCAPs are two broad interface-state-related bands centered around midgap, which appear to be very similar to what has been found in the past for other gate dielectrics on GaAs. At the same time, it is reported that the interface-state peak shifts closer to the conduction band for the InxGa1-xAs layers, whereby the activation energy becomes smaller for higher x. However, it is demonstrated that in this case not only interface states contribute to the DLTS emission signal but also deep levels associated with threading dislocations (TDs) in the relaxed layers. This contribution grows progressively with the In content, i.e., with the amount of relaxation. From this, it is concluded that InxGa1-xAs/GaAs substrates are not favorable for inversion-type of MOS devices due to the increasing impact of the TDs on the device performance.

Review—Device Assessment of Electrically Active Defects in High-Mobility Materials

“…145,[149][150][151][152][153] Besides p-n junctions, one can also rely on the use of a Metal-Oxide-Semiconductor (MOS) capacitor to investigate both bulk and interface defects in III-V layers by DLTS. 154 Such an exercise has been performed on MOS capacitors Note that a similar downshift of E A with x is well-known for grown-in defects in In x Ga 1-x As ternary alloys 145,152,153 and has been interpreted in terms of a fixed position with respect to the top of the valence band edge. 153 It suggests that the deep levels are mainly composed of As-related valence band states.…”

“…It is tempting to assign the deep levels in Fig. 24 to Al 2 O 3 / In x Ga 1-x As interface states, 154 which shift closer to the conduction band for increasing x. However, from the trap filling kinetics in Fig.…”

(Invited) On the Electrical Activity of Extended Defects in High-Mobility Channel Materials

“…It is tempting to assign the deep levels in Fig. 10 to Al 2 O 3 /In x Ga 1-x As interface states [45], which shift closer to the conduction band for increasing x. However, from the trap filling kinetics in Fig.…”

“…On the other hand, quite some DLTS investigations of as-grown material have been reported, revealing the electrically active deep levels of dislocations in, for example, GaAs [36][37][38][39] and In x Ga 1-x As [36,[40][41][42][43][44]. Besides p-n junctions, one can also rely on the use of a Metal-Oxide-Semiconductor (MOS) capacitor to investigate both bulk and interface defects in III-V layers by DLTS [45]. Such an exercise has been performed on MOS capacitors consisting of a 50 nm Pt gate on top of 10 nm Atomic Layer Deposited (ALD) Al 2 O 3 on 100 mm diameter n-or p-type GaAs substrates, with a doping density of ~5x10 17 cm -3 .…”