We demonstrate epitaxial β-Ga 2 O 3 /GaN-based vertical metal-heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UV-to-visible rejection >10 3 , and a photo-to-dark current ratio of >100. A small (large) conduction (valence) band offset at the heterojunction of pulsed laser deposition (PLD)-grown β-Ga 2 O 3 on metal organic chemical vapor deposition (MOCVD)grown GaN-on-silicon with epitaxial registry, as confirmed by X-ray diffraction (XRD) azimuthal scanning, is exploited to realize detectors with an asymmetric photoresponse and is explained with one-dimensional (1D) band diagram simulations. The demonstrated novel vertical MHM detectors on silicon are fully scalable and promising for enabling focal plane arrays for broadband ultraviolet sensing.
In this report, we demonstrate direct epitaxial integration of β-Ga 2 O 3 on a (400) oriented silicon on insulator substrate toward deep-UV (DUV) optoelectronics. The 550 nm thick (400) epitaxial-β-Ga 2 O 3 films are deposited onto Si(100) using a two-step buffer and a two-step epilayer scheme. The epitaxial orientation relation between β-Ga 2 O 3 , MgO, and silicon( 100) is given by (400The presence of rotational variants is confirmed by Xray diffraction and transmission electron microscopy. Epitaxy was found to be mediated through a MgGa 2 O 4 layer formed at the β-Ga 2 O 3 /MgO interface under oxygen-deficient conditions during pulsed layer deposition. The ω-scan symmetric and asymmetric full width at half-maximum values of β-Ga 2 O 3 are 2.41 and 2.39°, respectively. Photodetectors realized in a conventional metal− semiconductor−metal geometry exhibit a maximum responsivity of 11.8 A/W at 246 nm at 40 V with a photo to dark current ratio of 2.5 × 10 2 and a UV-to-visible rejection ratio > 10 3 . The detectors do not exhibit any persistent photoconductivity as is evident from the rise and fall times of 0.54 and 0.32 s, respectively. Such a monolithic integration of β-Ga 2 O 3 on Si(100) opens up opportunities for the development of integrated DUV focal plane arrays on a SoC chip.
The
integration of BaTiO3 with Si(100) is essential
to exploit its ferroelectric capabilities in the well-established
Si-complementary metal–oxide–semiconductor (CMOS) technological
platform. To enable this goal, epitaxial BaTiO3 films with
both in-plane and out-of-plane polarization are demonstrated on Si(100)
with just a single TiN layer that is also CMOS-compatible. This change
in polarization direction is brought about very simply by changing
the growth temperature. Piezo force microscopy and optical second-harmonic
generation measurements confirm the presence of out-of-plane and in-plane
polarization. Films deposited at relatively higher temperatures of
800 °C have polarization lying in-plane at room temperature.
The nonlinear dielectric susceptibilities were found to be comparable
to the state-of-the-art films integrated with more complex transition
schemes. Films deposited at a relatively lower temperature of 600
°C are defective and revert to 800 °C like films on annealing.
The defects however confer on them an out-of-plane polarization with
a large tetragonality of 1.6% at 500 °C. The changes in anomalous
lattice expansion in out-of-plane coupled with coefficient of thermal
expansion (CTE) strain result in orientation selection in our films.
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