Electrical properties of InAlP native oxides for metal–oxide–semiconductor device applications

Abstract

Data are presented on the insulating properties and capacitance-voltage (CV) characteristics of metal-oxide-semiconductor (MOS) device-thickness (below ~100 nm) native oxides formed by wet thermal oxidation of thin InAlP epilayers lattice matched to GaAs. Low leakage current densities of J=1.4 x 10 -9 A/cm 2 and J=8.7 x 10 -11 A/cm 2 are observed at an applied field of 1 MV/cm for MOS capacitors fabricated with 17 nm and 48 nm oxides, respectively. TEM images show that the In-rich interfacial particles which exist in 110 nm oxides are absent in 17 nm oxide films. Quasi-static capacitance-voltage measurements of MOS capacitors fabricated on both n-type and p-type GaAs show that the InAlP oxide-GaAs interface is sufficiently free of traps to 1 support inversion, indicating an unpinned Fermi level. These data suggest that InAlP native oxides may be a viable insulator for GaAs MOS device applications. 2Due to the wide array of high electron mobility alloys of varying bandgaps that can be epitaxially grown on its surface, GaAs remains the most widely used semiconductor for high-speed electronic applications. While Schottky gates are commonly used in high-speed GaAs transistors, the restricted forward bias (a few tenths of a volt) that can be applied without excessive gate leakage currents limits their power handling capability.The electrical characteristics of native oxides of GaAs are far inferior to those of SiO 2 on Si, and an alternative insulator has long been pursued 1,2 to enable the preferred metal-insulator-semiconductor gate structure. Many deposited insulator/GaAs structures have been investigated, although only a few have yielded promising results. 3-6 Native oxide films on GaAs can offer advantages of processing convenience and low cost.Wet thermal oxides of AlGaAs 7 have been studied but found to suffer from midgap traps caused by residual interfacial As. 8 These traps lead to increased interface recombination velocity 9,10 and high leakage currents. 11 However, the wet thermal oxides of As-free As shown in the bright-field TEM images of Fig. 2, dark particles exist near the oxide/GaAs interface in the 110 nm oxide of Fig. 2 (a), while no dark interfacial particles appear in the 17 nm oxide of Fig. 2 (b). Fig. 2 (b) is representative of the entire observable area for this and a second wedge-polished cross section specimen, with the absence of particles also confirmed for plan-view specimens (not shown) in which possible loss of particles due to ion milling and electron beam interactions is suppressed by the fact that they are protected from the vacuum by the substrate and overlying oxide film. The interfacial particles in Fig. 2 (a) are believed to be indium rich based on Z-contrast TEM images 16 (not shown) and Auger depth profiling. 17 The size of the particles increases with the progressive consumption of the InAlP epilayer during oxidation. 16 We hypothesize that In, the heaviest element in the structure, outdiffuses more slowly than the other alloy constituents and hence accumulates near the inter...

Microwave performance of GaAs MOSFET with wet thermally oxidized InAlP gate dielectric

“…These traps lead to increased interface recombination velocity [16], [17] and high-leakage currents [18], [19]. However, the wet thermal oxides of Asfree In 0.5 Al 0.5 P (lattice matched to GaAs) have been found to Manuscript possess excellent insulating [20]- [22] and interfacial properties [21], [23] and may provide a viable native oxide for III-V MOS devices. In this letter, we present the first demonstration of the microwave-frequency operation of a GaAs-based MOSFET using a native dielectric gate insulator formed through thermal oxidation.…”

Performance of Sub-micron Gate Length InAlP Native Oxide GaAs-channel MOSFETs

“…Among many candidate gate insulating materials (e.g. [1][2][3][4]), the native oxide of InAlP offers a low leakage current [4] and modest interface state density [5] while at the same time being simple to fabricate and offering a path to low-cost devices. Both enhancement-mode [6] and depletion-mode MOSFETs [7-8] with gate lengths ≥ 1 µm have been demonstrated with InAlP native oxide gate dielectrics.…”

Microwave-Frequency InAlP-oxide/GaAs MOSFETs

“…From Fig. 6, a leakage current density of 1.58 x 10-4 A/cm2 at 1 V bias is obtained for the MOS capacitor, demonstrating that the excellent insulating properties of the native InAlP oxide [7] are preserved as the oxide thickness is scaled to 7.5 nm. The lower leakage current density of the MOS capacitors relative to MOSFETs on the same heterostructure indicates a parasitic leakage path where the gate metallization runs over the etched mesa edges of the FET structures [10].…”

“…For gate oxide formation, the regions in which the gate oxide is to be formed are defined using optical lithography, followed by selective wet-chemical etching to remove the GaAs cap layer in these regions using a citric acid/hydrogen peroxide solution. This etching exposes the InAlP layer, which is then oxidized at 440°C for 30 minutes in a water vapor ambient [7]. The InAlP native oxide thickness, measured via transmission electron microscopy as shown in Fig of the GaAs channel after oxidation are measured to be 9.39x1011 cm-2, and 3310 cm2/V-s, respectively.…”

“…Many candidate insulating materials on GaAs have been explored, with only a few showing promising results [1][2][3][4]. Of these, the native oxide of InO5AI05P is known to be an excellent insulator suitable for MOS applications [5][6][7]. The wet thermal oxidation of InAlP on GaAs can result in an oxidesemiconductor interface with unpinned Fermi level and low interface state density [6,8].…”