F. Gucmann

InGaAs/GaAs metal-oxide-semiconductor heterostructure field-effect transistors with oxygen-plasma oxide and Al2O3 double-layer insulator

Surface condition before an insulator deposition is the key issue for the preparation of reliable GaAs-based metal-oxide-semiconductor (MOS) devices. This study presents the preparation and properties of InGaAs/GaAs MOS structures with a double-layer insulator consisting of an oxygen-plasma oxide covered by Al2O3. The structures were oxidized during 75 s and 150 s. Static measurements yielded a saturation drain current of ∼250 mA/mm at VG = 1 V. Capacitance measurements showed improved performance in the depletion region compared with the structures without the double-layer insulator. Trapping effects were investigated by conductance vs. frequency measurements. The trap state density was in order of 1011 cm−2·eV−1 with a continuous decrease with increased trap energy. The carrier mobility evaluation showed peak values of 3950 cm2/V·s for 75 s and 4570 cm2/V·s for 150 s oxidation times with the sheet charge density ≅2 × 1012 cm−2. The results demonstrate great potential of the procedure that was used to pr...

Low-temperature atomic layer deposition-grown Al2O3 gate dielectric for GaN/AlGaN/GaN MOS HEMTs: Impact of deposition conditions on interface state density

The oxide/semiconductor interface state density (Dit) in Al2O3/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with gate oxides grown by atomic layer deposition at low deposition temperature is analyzed in this work. MOS-HEMT structures with Al2O3 gate oxide were deposited at 100 and 300 °C using trimethylaluminum precursor and H2O and O3 oxidation agents. The structures were found to show negative net charge at oxide/barrier interface with density (Nint) of 1013 cm−2, which was attributed to the reduction of barrier surface donor density (NDS). Dit was determined using capacitance transient techniques, and the results were assessed by the simulations of the capacitance–voltage characteristics affected by interface traps. The results indicate a lower interface quality of the sample with Al2O3 grown using O3 agent compared to those with H2O, even though the former provided lowest gate leakage among the analyzed structures. Moreover, to uncover the NDS nature, Dit...

Optimization of UV-assisted wet oxidation of GaAs

Ultraviolet (UV) light-assisted wet oxidation in deionized water (photowashing) was done on commercial semi-insulating (SI) and N-type (Nd ∼ 7.5 × 1017 cm−3) (100) GaAs substrates. Oxidation rate, depth elemental composition profiling, and structural quality of prepared oxide layers and oxide/GaAs interfaces were evaluated for various oxidation times and for four selected intensities of UV light (320–480 nm) irradiation by means of x-ray reflectivity, x-ray photoelectron spectroscopy, and transmission electron microscopy (TEM), respectively. N-type GaAs exhibited ∼30% higher oxidation rates as compared to SI GaAs. Oxidized layers were found to consist predominantly of Ga2O3. Peak gallium concentrations in oxidized layers related to Ga2O3 achieved ∼45 at. %, while concentrations of arsenic related to unfavorable As2O3 were found to be as low as 4–5 and 4–6 at. % for SI GaAs and N-type GaAs, respectively. As2O3 occurrence was not spatially confined and occurred throughout the oxidized layer. Arsenic depth c...

Effect of HCl pretreatment on the oxide/semiconductor interface state density in AlGaN/GaN MOS-HEMT structures with MOCVD grown A1 2 O 3 gate dielectric

Suppression of surface donors (SDs) in AlGaN/GaN MOS-HEMTs represents a promising approach towards realization of normally-off switching devices with high threshold voltage. In this work, density of oxide/barrier interface traps (Dit) was determined in AlGaN/GaN MOS-HEMT structures with different SDs density (Nds), resulted from HCl pre-treatment variation. The results suggest deteriorated interface quality for sample without HCl cleaning. Dit was found to increase from ~1012 to ~1013 eV-1 cm-2 in the energy range of 0.8 to 1.1 eV below the conduction band edge for structures with and without HCl cleaning step, respectively. On the other hand, our analysis indicates negligible contribution of interface traps to observed threshold voltage in thermal equilibrium. This indicates the nature of SDs to be different from that of interface traps.

Threshold voltage instabilities in AlGaN/GaN MOS-HEMTs with ALD-grown Al 2 O 3 gate dielectrics: Relation to distribution of oxide/semiconductor interface state density

Metal-oxide-semiconductor (MOS) structure represents an important gate technology in GaN HEMTs. As oxide/semiconductor interface quality is remaining reliability concern, several techniques for determination of interface state density (D_it) has been proposed. In the literature, the hysteresis in C-V sweeps (or V_th shift, ΔV_th) is often interpreted as D_it in particular energy range in the semiconductor band-gap. In this work, we critically assessed a relevancy of relation between ΔV_th (measured at 25 and 125 ^°C) and experimentally determined D_it distribution, to point out possible pitfalls in the data interpretation. D_it distributions were measured by combination of complementary techniques and ID simulations applied to state-of-the-art MOS-HEMTstructures with Al₂O₃ films grown by ALD on AlGaN/GaN heterostructures. It is demonstrated that, apart from interface traps, also other parasitic effects related to border traps and oxide bulk traps can have dominant impact on ΔV_th-This means that ΔV_th could not be solely related to D_it, unless negligibility of other relevant effects is confirmed.

DC and pulsed IV characterisation of AlGaN/GaN MOS-HEMT structures with Al 2 O 3 gate dielectric prepared by various techniques

AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) represent an important technology for future high-efficient power and RF electronics. Due to oxide/semiconductor interface issues, fabrication of reliable MOS gate stack is still challenging, however. In this work we investigated the influence of gate oxide preparation technique to static and pulsed-mode operation of Al₂O₃/GaN/AlGaN/GaN MOS-HEMTs. Devices with gate oxide prepared by high-temperature MOCVD and low-temperature ALD using water vapour or ozone as oxidants are compared in terms of dynamic on-state resistance (R_DSon), threshold voltage shift (ΔV_th), and Al₂O₃/GaN interface charge density (N_it).

Nucleation and annihilation of magnetic vortices in Pacman-like nanodots observed by micro-Hall probes

We have used micro-Hall probe for the study of vortex dynamics in micromagnetic objects with lowered symmetry. The Pacman-like nanodot of the diameter of 1 μm was placed directly on the Hall probe and the signal was red in band resistance configuration. We show that the vortex nucleation and annihilation, as well as s-and c-state creation/annihilation are clearly visible on the magnetization reversal characteristics at 77 K. The experimental characteristics is in good agreement with the one calculated by micromagnetic simulations.

Distribution of fixed oxide charge in MOS structures with ALD grown Al 2 O 3 studied by capacitance measurements

We analyze the fixed oxide charge in Al₂O₃ grown by thermal and plasma enhanced ALD at 100 and 200 °C using capacitance-voltage measurements on MOS structures with different Al₂O₃ thickness. For both ALD techniques and deposition temperatures, Al₂O₃ shows negative fixed oxide charge with density in the range of 2-7×10¹² cm^-2, most likely located at the Al₂O₃/SiO₂ interface as inferred from the linear dependence of flat-band voltage on Al₂O₃ thickness. The break-down field ranges from 4 to 8 MV/cm illustrating a high quality of the Al₂O₃ layers. Post-deposition annealing was found to stabilize the Al₂O₃ dielectric constant determined to be similar to 9. Control of the negative Al₂O₃ fixed charge represents a promising way to e.g. enhance the threshold voltage shift of GaN based MOS heterostructure FETs towards normally-off operation.

Properties of Al2O3 thin films grown by atomic layer deposition

Thin Al₂O₃ films were prepared by thermal and plasma enhanced atomic layer deposition at 100 and 200°C. Growth per cycle ranges from 0.108 to 0.139 nm/cycle. Composition of the films was investigated by XPS. Carbon impurity was higher for the films grown at 100°C. The films grown at 200°C were slightly oxygen deficient.The Al₂O₃ films grown at low temperatures have promising applications in microelectronics.

The influence of an AlO x film in-situ deposited on the GaAs-based HFETs properties

An in-situ deposited AlOx layer has a great influence on the transistor properties. We recently published a comparison between an AlGaAs/InGaAs/GaAs HFET (without any passivation) and a passivated MOSHFET (AlOx/AlGaAs/InGaAs/GaAs. This paper reports on properties of AlGaAs/GaAs transistors with an InGaAs channel passivated with an in-situ deposited AlOx layer. Also, the effectiveness of the passivation is discussed. The influence of an thin AlOx layer on properties of passivated HFET in comparison to the passivated MOSHFET and the unpassivated HFET was studied. The understanding of the functionality of the in-situ deposited layer in the passivation or modification of surface trapping states will contribute to the knowledge of GaAs surface potential control.