Study of Phase Transition in MOCVD Grown Ga2O3 from κ to β Phase by Ex Situ and In Situ Annealing

Lee, Junhee; Kim, Honghyuk; Gautam, Lakshay; He, Kun; Hu, Xiaobing; Dravid, Vinayak P.; Razeghi, Manijeh

doi:10.3390/photonics8010017

Cited by 21 publications

(26 citation statements)

References 20 publications

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“…The three peaks that were observed were similar to the results of the β-Ga 2 O 3 substrate (Figure 1). However, the TEM analysis in Figure 1d showed the result of κ-phase with the space group of Pna2 1 [4,5,10]. This metastable and transient κ-Ga 2 O 3 was also identified by Playford et al [13].…”

Section: Resultsmentioning

confidence: 59%

“…Moreover, the relatively low thermal conductivity of Ga 2 O 3 and the problem of Ga 2 O 3 substrate cost being two orders of magnitude higher than sapphire are both currently hindering the fuller development of Ga 2 O 3 -based powered electronics. In previous studies, we showed that κ-Ga 2 O 3 (an orthorhombic polymorph which is normally considered to be transient) could be stabilized in heteroepitaxial growth on sapphire (0001) substrates by MOCVD [4][5][6][7][8][9][10][11][12]. In this work, we found that high levels of shallow acceptor p-type conduction could be achieved in such layers using silicon impurity doping under Ga rich growth conditions.…”

Section: Introductionmentioning

confidence: 80%

“…The VI/III ratio was either 100 (Ga-rich) or 150 (O-rich). The SiH4 flow rate was fixed at 15 sccm [4][5][6][7][8][9][10][11][12].…”

Section: Methodsmentioning

confidence: 99%

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Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD

et al. 2021

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Gallium oxide (Ga2O3) thin films of various thicknesses were grown on sapphire (0001) substrates by metal organic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa), high purity deionized water, and silane (SiH4) as gallium, oxygen, and silicon precursors, respectively. N2 was used as carrier gas. Hall measurements revealed that films grown with a lower VI/III ratio had a dominant p-type conduction with room temperature mobilities up to 7 cm2/Vs and carrier concentrations up to ~1020 cm−3 for thinner layers. High resolution transmission electron microscopy suggested that the layers were mainly κ phase. Microstrip field-effect transistors (FETs) were fabricated using 2D p-type Ga2O3:Si, channels. They achieved a maximum drain current of 2.19 mA and an on/off ratio as high as ~108. A phenomenological model for the p-type conduction was also presented. As the first demonstration of a p-type Ga2O3, this work represents a significant advance which is state of the art, which would allow the fabrication of p-n junction based devices which could be smaller/thinner and bring both cost (more devices/wafer and less growth time) and operating speed (due to miniaturization) advantages. Moreover, the first scaling down to 2D device channels opens the prospect of faster devices and improved heat evacuation.

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Section: Resultsmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 80%

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Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD

et al. 2021

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“…Figure 1 shows the top-view FESEM images of the Ga2O3 films on the c-plane (0001) sapphire substrates. None of the as-deposited and annealed Ga2O3 films had extended cracks after the ex situ annealing process using the RTA system [23]. The as-deposited film showed that the surface morphologies comprised fine grains tightly connected with a relatively clear boundary, as shown in Figure 1a.…”

Section: Resultsmentioning

confidence: 99%

Magnetron Sputter-Deposited β-Ga2O3 Films on c-Sapphire Substrate: Effect of Rapid Thermal Annealing Temperature on Crystalline Quality

Pech

Kim

2022

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Gallium oxide (Ga2O3) is a semiconductor with a wide bandgap of ~5.0 eV and large breakdown voltages (>8 MV·cm−1). Among the crystal phases of Ga2O3, the monoclinic β-Ga2O3 is well known to be suitable for many device applications because of its chemical and thermal stability. The crystalline quality of polycrystalline β-Ga2O3 films on c-plane sapphire substrates was studied by rapid thermal annealing (RTA) following magnetron sputtering deposition at room temperature. Polycrystalline β-Ga2O3 films are relatively simple to prepare; however, their crystalline quality needs enhancement. The β-phase was achieved at 900 °C with a crystallite size and d-spacing of 26.02 and 0.2350 nm, respectively, when a mixture of ε- and β-phases was observed at temperatures up to 800 °C. The strain was released in the annealed Ga2O3 films at 900 °C; however, the clear and uniform orientation was not perfect because of the increased oxygen vacancy in the film at that temperature. The improved polycrystalline β-Ga2O3 films with dominant (−402)-oriented crystals were obtained at 900 °C for 45 min under a N2 gas atmosphere.

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“…Regarding the oxygen precursor, commonly used O 2 is the established choice, yet the use of N 2 O can lead to a lower background charge carrier concentration [ 21 ] and the use of water (H 2 O) vapour can potentially have a positive effect on the kinetic conditions during film growth due to the presence of hydrogen [ 20 ]. There are only a few papers reporting the use of H 2 O as an oxygen precursor; Alema et al demonstrated a reduction in carrier concentration by adding a small amount of H 2 O to the O 2 flow during the film growth [ 22 ], while Lee et al and Chen et al reported Ga 2 O 3 film growth using H 2 O as the oxygen precursor without further discussions on the choice [ 23 , 24 , 25 ].…”

Section: Introductionmentioning

confidence: 99%

The Effect of a Nucleation Layer on Morphology and Grain Size in MOCVD-Grown β-Ga2O3 Thin Films on C-Plane Sapphire

et al. 2022

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β-Ga2O3 thin films grown on widely available c-plane sapphire substrates typically exhibit structural defects due to significant lattice and thermal expansion mismatch, which hinder the use of such films in electronic devices. In this work, we studied the impact of a nucleation layer on MOCVD-grown β-Ga2O3 thin film structure and morphology on a c-plane sapphire substrate. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, transmission and scanning electron microscopy, while the composition was confirmed by X-ray photoelectron spectroscopy and micro-Raman spectroscopy. It was observed that the use of a nucleation layer significantly increases the grain size in the films in comparison to the films without, particularly in the samples in which H2O was used alongside O2 as the oxygen source for the nucleation layer growth. Our study demonstrates that a nucleation layer can play a critical role in obtaining high quality β-Ga2O3 thin films on c-plane sapphire.

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Study of Phase Transition in MOCVD Grown Ga2O3 from κ to β Phase by Ex Situ and In Situ Annealing

Cited by 21 publications

References 20 publications

Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD

Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD

Magnetron Sputter-Deposited β-Ga2O3 Films on c-Sapphire Substrate: Effect of Rapid Thermal Annealing Temperature on Crystalline Quality

The Effect of a Nucleation Layer on Morphology and Grain Size in MOCVD-Grown β-Ga2O3 Thin Films on C-Plane Sapphire

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