We report on our investigation of the electrical properties of metal/Al2O3/GaN metal-insulator-semiconductor capacitors. We determined the conduction band offset and interface charge density of the alumina/GaN interface by analyzing the capacitance-voltage characteristics of atomic layer deposited Al2O3 films on GaN substrates. The conduction band offset at the Al2O3/GaN interface was calculated to be 2.13 eV, in agreement with theoretical predications. A non-zero field of 0.93 MV/cm in the oxide under flat-band conditions in the GaN was inferred, which we attribute to a fixed net positive charge density of magnitude 4.60 × 1012 cm−2 at the Al2O3/GaN interface. We provide hypotheses to explain the origin of this charge by analyzing the energy band line-up.

https://chppe.osu.edu/sites/chppe.osu.edu/files/uploads/Publications3/Electrical%20properties%20of%20atomic%20layer%20deposited%20aluminum%20oxide%20on%20gallium%20nitride.pdf

Electrical properties of atomic layer deposited aluminum oxide on gallium nitride

The effects of Al2O3 gate insulator grown by atomic layer deposition (ALD) system on the two-dimensional electron gas (2DEG) transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. The shape of the electron lateral distribution in the quantum well at AlGaN/GaN interface was found to be slightly influenced by the Al2O3 thin layer. The drift mobility (μd) of the electrons in ALD-Al2O3/AlGaN/GaN MISHEMT is increased due to the surface passivation effects of the included dielectric layer. The higher dynamic channel current of the MISHEMT indicates that the electron saturation velocity (vsat) is also increased. These results show the improvement of the transport characteristics of 2DEG in Al2O3/AlGaN/GaN MISHEMT by the excellent properties of the Al2O3 grown by ALD.

Improved two-dimensional electron gas transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor with atomic layer-deposited Al2O3 as gate insulator

We report on frequency dependent capacitance and conductance analysis of the AlGaN/GaN/Si heterostructure field-effect transistors (HFETs) and Al2O3/AlGaN/GaN/Si metal-oxide-semiconductor HFETs (MOSHFETs) in order to investigate the trap effects in these devices. The capacitance of the HFETs exhibits significantly higher frequency dispersion than that of the MOSHFETs. Two different types of traps were found from the conductance analysis on both types of devices, fast with the time constant τ≅(0.1–1) μs and slow with τ=8 ms. The density of trap states evaluated on the HFETs was DT≅2.5×1012 and up to 1013 cm−2 eV−1 for the fast and slow traps, respectively. Analysis of the MOSHFETs yielded only slightly lower DT of the fast traps (≅1.5×1012 cm−2 eV−1), but nearly two orders of magnitude lower density of slow traps (≤4×1011 cm−2 eV−1) than those of the HFETs. This indicates an effective passivation of slow surface related traps but less influence on fast (probably bulk related) trapping states by applying an insulator on the AlGaN/GaN HFET.

Investigation of trapping effects in AlGaN/GaN/Si field-effect transistors by frequency dependent capacitance and conductance analysis

This letter describes a gate-first AlGaN/GaN high-electron mobility transistor (HEMT) with a W/high-k dielectric gate stack. In this new fabrication technology, the gate stack is deposited before the ohmic contacts, and it is optimized to stand the 870degC ohmic contact annealing. The deposition of the W/high-k dielectric protects the intrinsic transistor early in the fabrication process. Three different gate stacks were studied: W/ HfO2, W/Al2O3, and W/HfO2/Ga2O3. DC characterization showed transconductances of up to 215 mS/mm, maximum drain current densities of up to 960 mA/mm, and more than five orders of magnitude lower gate leakage current than in the conventional gate-last Ni/Au/Ni gate HEMTs. Capacitance-voltage measurements and pulsed-IV characterization show no hysteresis for the W/HfO2/ Ga2O3 capacitors and low interface traps. These W/high-k dielectric gates are an enabling technology for self-aligned AlGaN/GaN HEMTs, where the gate contact acts as a hard mask to the ohmic deposition.

/pdf/gate-first-algan-gan-hemt-technology-for-high-frequency-4xc00yvjh7.pdf

Gate-First AlGaN/GaN HEMT Technology for High-Frequency Applications

Interface charges at atomic layer deposited Al2O3/III-nitride interfaces were investigated for III-nitride layers of different polarity. A large positive sheet charge density is induced at the Al2O3/III-nitride interface on all the orientations of GaN and Ga-polar AlGaN, and this sheet charge can be significantly altered using post-metallization anneals. It is proposed that the charges are caused by interfacial defects that can be passivated and neutralized through a H2 based anneal. Tailoring of the interface charge density described here can be used to improve critical device characteristics such as gate leakage and electron transport, and for lateral electrostatic engineering.

Interface charge engineering at atomic layer deposited dielectric/III-nitride interfaces

The Al 2 O 3 as a gate oxide and passivation was used to study the transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOSHFETs). Performance of the devices with Al 2 O 3 of different thickness between 4 and 14 nm prepared by metal–organic chemical vapor deposition (MOCVD) and with 4 nm thick Al 2 O 3 prepared by Al sputtering and oxidation was investigated. All MOS-devices yielded higher transconductance than their HFET counterparts, i.e. the transconductance/capacitance expected proportionality assuming the same carrier velocity was not fulfilled. A different electric field near/below the gate contact due to a reduction of traps is responsible for the carrier velocity enhancement in the channel of the MOSHFET. The trap reduction depends on the oxide used, as follows from the capacitance vs frequency dispersion for devices investigated. It is qualitatively in a good agreement with the different velocity enhancement evaluated, and devices with thinner oxide show higher traps reduction as well as higher transconductance enhancement. It is also shown that obtained conclusions can be applied well on performance of SiO 2 /AlGaN/GaN MOSHFETs.

Transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with Al2O3 of different thickness

Frequency dependent conductance measurements at varied temperature between 25 and 260 °C were performed to analyze trapping effects in the Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors. The trap states with a time constant τT,f≅(0.1–1) μs (fast) and τT,s=10 ms (slow) were identified. The conductance measurements at increased temperatures made it possible to evaluate the fast trap states in about a four times broader energy range than that from room temperature measurement. The density of the fast traps decreased from 1.4×1012 cm−2 eV−1 at an energy of 0.27 eV to about 3×1011 cm−2 eV−1 at ET=0.6 eV. The density of the slow traps was significantly higher than that of the fast traps, and it increased with increased temperature from about 3×1012 cm−2 eV−1 at 25–35 °C to 8×1013 cm−2 eV−1 at 260 °C.

Trapping effects in Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistor investigated by temperature dependent conductance measurements

We investigate the complex conductivity of a highly disordered MoC superconducting film with k(F)l approximate to 1, where k(F) is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature T-c. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, tau, offers a perfect description of the experimentally observed complex conductivity. We show that iota is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

Finite quasiparticle lifetime in disordered superconductors

The reactive magnetron sputtering technique at room temperature was used to prepare AlN dielectric layer for application in AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs). Two different gas ambiences (mixture of nitrogen and argon N2/Ar=0.35 and N2 alone, respectively) were applied. An increase in the saturation drain current (∼50%) and transconductance (∼45%) of the MIS-HFETs compared with HFET counterparts (IDS=363 mA/mm and gm=114 mS/mm) was observed. AlN/AlGaN/GaN MIS-HFET, where only the nitrogen gas ambience was used to deposit an AlN dielectric layer, reduced the gate leakage current up to four orders of magnitude (∼10−8 A/mm at −5 V) in comparison with the HFET. The improvements of the dynamic characteristics of the MIS-HFETs (reduction of the current collapse and density of the slow traps) were achieved. The N2 MIS-HFET exhibits better improvements of the static and dynamic parameters than the ArN2 MIS-HFET, and therefore the deposition of the AlN lay...

Performance of AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors with AlN gate insulator prepared by reactive magnetron sputtering

Š. Gaži

Papers

Transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with Al2O3 of different thickness

Trapping effects in Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistor investigated by temperature dependent conductance measurements

Finite quasiparticle lifetime in disordered superconductors

Performance of AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors with AlN gate insulator prepared by reactive magnetron sputtering

Superconducting MoC thin films with enhanced sheet resistance