Experimental band alignment of Ta2O5/GaN for MIS-HEMT applications

Sawangsri, K.; Das, P.; Supardan, Siti Nurbaya; Mitrović, Ivona Z.; Hall, S.; Mahapatra, Rajat; Chakraborty, Amit; Treharne, Robert E.; Gibbon, James T.; Dhanak, Vin; Durose, K.; Chalker, Paul R.

doi:10.1016/j.mee.2017.04.010

Cited by 9 publications

(8 citation statements)

References 30 publications

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“…Regarding the fitting procedure for the Ga 3d peak, most publications use one peak that encompasses the Ga 3d 5/2 and Ga 3d 3/2 doublet, generally positioned between 19.3 to 20.3 eV for Ga-N bond [28][29][30][31][32] . In this work, each Ga 3d component is fitted with a doublet using a spin-orbit splitting of 0.45 eV and an area ratio between the d 5/2 and d 3/2 components of 0.66 [33][34][35][36] . The XPS spectra of the pristine GaN is calibrated in energy by fixing the C-C peak position of the carbon contamination at 284.8 eV.…”

Section: B Xps Fitting Proceduresmentioning

confidence: 99%

Influence of the carrier wafer during GaN etching in Cl2 plasma

Meyer

Petit-Etienne

Pargon

2022

Journal of Vacuum Science &Amp; Technology A

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In this study, we have performed a thorough characterization of the GaN surface after etching up to 100 nm in Cl2 plasma under various bias voltages and according to the carrier wafer used (Si, SiO2, Si3N4, and photoresist). The objective of this article is to evaluate the etch damage and contamination of the GaN surface when materials with other chemical nature are present during etching. The effects of etching conditions on surface morphology and chemical compositions of etched GaN films are studied in detail using XPS and AFM measurements. To this aim, a universal methodology is proposed to estimate accurately by XPS the stoichiometry of the GaN surface exposed to reactive plasmas when only an Al Kα x-ray source is available. The results indicate that the GaN etching mechanisms are very sensitive to the chlorine radical density present in the plasma, the latter being strongly influenced by the carrier wafer. Substrates that are more chemically reactive with Cl2 plasma such as silicon or photoresist compared to SiO2 or Si3N4 will lead to a greater loading of atomic chlorine, which in turn will lead to lower GaN etch rates. Moreover, the GaN surface contamination will depend on the etch by-products ejected by the carrier wafer. The GaN surface exposed to Cl2 plasma shows a Ga-depleted surface because of the more important reactivity of Cl with Ga rather than N, except in the SiO2 carrier wafer case. In this latter case, the formation of Ga–O bond limits the Ga removal. Regarding the surface roughness, it seems that the contaminants play a little role in the roughness formation except for the oxygen released by the SiO2 carrier wafer. On the other hand, the surface roughness evolution is clearly driven by the chlorine radical flux reaching the GaN surface. At low bias voltage, a preferential crystalline orientation etching driven by the Cl radicals leads to the formation of hexagonal shaped defects that are associated to screw-type threading dislocations already present in the pristine GaN material. At higher bias, the enlargement of the defects is limited, leading to a very low surface roughness value but to amorphized surfaces.

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Section: B Xps Fitting Proceduresmentioning

confidence: 99%

Influence of the carrier wafer during GaN etching in Cl2 plasma

Meyer

Petit-Etienne

Pargon

2022

Journal of Vacuum Science &Amp; Technology A

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“…The Kraut method is frequently used to experimentally determine the band alignments at semiconductor interfaces [36][37][38] . This method uses the photoelectron spectra of a series of three samples to determine the band offsets at an interface, namely a thick overlayer sample (buffer), a substrate sample (CZTSSe) and an interfacial sample in which the core-levels from both the substrate and the overlayer (buffer/CZTSSe) are visible.…”

Section: A Band Alignment At Buffer/cztsse Interfacementioning

confidence: 99%

Defect limitations in Cu2ZnSn(S, Se)4 solar cells utilizing an In2S3 buffer layer

Campbell

Gibbon

et al. 2020

Journal of Applied Physics

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Alternative n-type buffer layer such as In 2 S 3 have been proposed as Cd-free alternative in kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells. In this study, optical and electronic characterisation techniques together with device analysis and simulation were used to assess nanoparticle-based CZTSSe absorbers and solar cells with CdS and In 2 S 3 buffers. Photoluminescence spectroscopy indicated CZTSSe absorbers with In 2 S 3 buffer had a lower density of detrimental non-radiative defects and a higher concentration of copper vacancies V Cu + , responsible for p-type conductivity in CZTSSe, in comparison to the absorber with CdS buffer. Capacitance-voltage (C-V) measurements revealed the In 2 S 3 buffer-based CZTSSe devices had a three times higher apparent doping density and a consequently narrower space charge region than devices with a CdS layer. This resulted in poorer collection of photo-generated charge carriers in the near-IR region despite a more favourable band alignment as determined by X-ray photoelectron and inverse photoelectron spectroscopy. The presence of interfacial defect states in In 2 S 3 devices as determined by C-V and biased quantum efficiency measurements are also responsible for the loss in open-circuit voltage compared with reference devices with CdS.

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“…Prior to oxide deposition, the GaN surface was cleaned using the following sequence: acetone for 10 min in an ultrasonic bath, 10 min in methanol, 20 min in 37% HCl solution and finally a deionised (DI) water rinse. Our previous work shows that the HCl treatment is effective in removing oxygen and carbon contaminant on the GaN surface [37] and the organic solvents serve to degrease the surface. For ZrO 2 deposition, the plasma power used was 25 W with oxygen and argon flow rates of 0.6 sccm and 1.4 sccm, respectively.…”

Section: Sample Fabrication and Cleaning Procedures Of Ganmentioning

confidence: 99%

“…The plasma power used for ZrO 2 and MgO deposition was 60 W, while for Al 2 O 3 it was 45 W with the chamber pressure of 1 × 10 −3 mbar at room temperature. The sputtering deposition rate was 0.07 Å s −1 for the interfacial ZrO 2 and Al 2 O 3 samples with thicknesses of 1.9 nm, 3.8 nm and 4.0 nm for the former and 2.5 nm, 4.4 nm and 6.9 nm for the latter oxide measured by variable angle spectroscopic ellipsometry (VASE) using a Cauchy model [37]. For MgO, the deposition rate of 0.16 Å s −1 was used to fabricate interfacial samples with thicknesses of 3.4 nm, 5.8 nm and 6.8 nm as measured by VASE.…”

Section: Sample Fabrication and Cleaning Procedures Of Ganmentioning

confidence: 99%

Band alignments of sputtered dielectrics on GaN

Supardan

Das

Major

et al. 2019

J. Phys. D: Appl. Phys.

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The band alignments of sputtered ZrO2, Al2O3 and MgO on GaN have been measured experimentally using x-ray photoelectron spectroscopy (XPS). The valence band offsets (±0.2 eV) for ZrO2, Al2O3 and MgO on GaN using Kraut’s method and charge-corrected XPS core levels were found to be 0.4 eV, 1.1 eV and 1.2 eV with corresponding conduction band offsets (±0.2 eV) of 1.3 eV, 2.0 eV and 2.8 eV, respectively. The electrical characterization of metal insulator semiconductor (MIS)-capacitors with different gate dielectrics (ZrO2, Al2O3 and MgO) has been performed as well. The current density of the MIS-capacitors with gate dielectrics MgO and Al2O3 at a positive bias of 1 V show lower leakage currents of 3.2 × 10−6 A cm−2 and 5.3 × 10−6 A cm−2 respectively, whereas, the MIS-capacitors with ZrO2 gate dielectric have the highest leakage current of 6.2 × 10−4 A cm−2 at 1 V.

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Experimental band alignment of Ta2O5/GaN for MIS-HEMT applications

Cited by 9 publications

References 30 publications

Influence of the carrier wafer during GaN etching in Cl2 plasma

Influence of the carrier wafer during GaN etching in Cl2 plasma

Defect limitations in Cu2ZnSn(S, Se)4 solar cells utilizing an In2S3 buffer layer

Band alignments of sputtered dielectrics on GaN

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