Ultrathin (1–4 nm) films of wide-bandgap semiconductors are important to many applications in microelectronics, and the film properties can be sensitively affected by defects especially at the substrate/film interface. Motivated by this, an in vacuo atomic layer deposition (ALD) was developed for the synthesis of ultrathin films of Ga2O3/Al2O3 atomic layer stacks (ALSs) on Al electrodes. It is found that the Ga2O3/Al2O3 ALS can form an interface with the Al electrode with negligible interfacial defects under the optimal ALD condition whether the starting atomic layer is Ga2O3 or Al2O3. Such an interface is the key to achieving an optimal and tunable electronic structure and dielectric properties in Ga2O3/Al2O3 ALS ultrathin films. In situ scanning tunneling spectroscopy confirms that the electronic structure of Ga2O3/Al2O3 ALS can have tunable bandgaps (Eg) between ∼2.0 eV for 100% Ga2O3 and ∼3.4 eV for 100% Al2O3. With variable ratios of Ga:Al, the measured Eg exhibits significant non-linearity, agreeing with the density functional theory simulation, and tunable carrier concentration. Furthermore, the dielectric constant ε of ultrathin Ga2O3/Al2O3 ALS capacitors is tunable through the variation in the ratio of the constituent Ga2O3 and Al2O3 atomic layer numbers from 9.83 for 100% Ga2O3 to 8.28 for 100% Al2O3. The high ɛ leads to excellent effective oxide thickness ∼1.7–2.1 nm for the ultrathin Ga2O3/Al2O3 ALS, which is comparable to that of high-K dielectric materials.
The new oxide paradigm for solid state ultraviolet photodetectors
The bandgap of wurzite ZnO layers grown on 2 inch diameter c-Al2O3 substrates by pulsed laser deposition was engineered from 3.7 to 4.8 eV by alloying with Mg. Above this Mg content the layers transformed from single phase hcp to mixed hcp/fcc phase before becoming single phase fcc above a bandgap of about 5.5 eV. Metal-Semiconductor-Metal (MSM) photodetectors based on gold Inter-Digitated-Transducer structures were fabricated from the single phase hcp layers by single step negative photolithography and then packaged in TO5 cans. The devices gave over 6 orders of magnitude of separation between dark and light signal with solar rejection ratios (I270 : I350) of over 3 x 105 and dark signals of 300 pA (at a bias of -5V). Spectral responsivities were engineered to fit the “Deutscher Verein des Gas- und Wasserfaches” industry standard form and gave over two decade higher responsivities (14 A/W, peaked at 270 nm) than commercial SiC based devices. Homogeneous Ga2O3 layers were also grown on 2 inch diameter c-Al2O3 substrates by PLD. Optical transmission spectra were coherent with a bandgap that increased from 4.9 to 5.4 eV when film thickness was decreased from 825 to 145 nm. X-ray diffraction revealed that the films were of the β-Ga2O3 (monoclinic) polytype with strong (-201) orientation. β-Ga2O3 MSM photodetectors gave over 4 orders of magnitude of separation between dark and light signal (at -5V bias) with dark currents of 250 pA and spectral responsivities of up to 40 A/W (at -0.75V bias). It was found that the spectral responsivity peak position could be decreased from 250 to 230 nm by reducing film thickness from 825 to 145 nm. This shift in peak responsivity wavelength with film thickness (a) was coherent with the apparent bandgap shift that was observed in transmission spectroscopy for the same layers and (b) conveniently provides a coverage of the spectral region in which MgZnO layers show fcc/hcp phase mixing.
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- Award ID(s):
- 1748339
- NSF-PAR ID:
- 10060452
- Date Published:
- Journal Name:
- Oxide-based Materials and Devices IX
- Volume:
- 105331P
- Issue:
- 105331P
- Page Range / eLocation ID:
- 105331P
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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α-Ga2O3 has the corundum structure analogous to that of α-Al2O3. The bandgap energy of α-Ga2O3 is 5.3 eV and is greater than that of β-Ga2O3, making the α-phase attractive for devices that benefit from its wider bandgap. The O-H and O-D centers produced by the implantation of H+ and D+ into α-Ga2O3 have been studied by infrared spectroscopy and complementary theory. An O-H line at 3269 cm-1 is assigned to H complexed with a Ga vacancy (VGa), similar to the case of H trapped by an Al vacancy (VAl) in α-Al2O3. The isolated VGa and VAl defects in α-Ga2O3 and α-Al2O3 are found by theory to have a “shifted” vacancy-interstitial-vacancy equlibrium configuration, similar to VGa in β-Ga2O3 which also has shifted structures. However, the addition of H causes the complex with H trapped at an unshifted vacancy to have the lowest energy in both α-Ga2O3 and α-Al2O3.more » « less
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R ) of over 0.4 A W−1, high specific detectivity (D* ) of over 1012Jones in the near‐infrared region under −0.2 V. Such highly sensitive broadband response PPDs, which can work well as self‐powered conditions, offer great potential applications in multicolor light detection. -
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2319505
