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Register a new userLateral Heterojunction BaTiO3/AlGaN Diodes with >8MV/cm Breakdown Field
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In this paper, we report enhanced breakdown characteristics of Pt/BaTiO3/Al0.58Ga0.42N lateral heterojunction diodes compared to Pt/Al0.58Ga0.42N Schottky diodes. BaTiO3, an extreme dielectric constant material, has been used, in this study, as dielectric material under the anode to significantly reduce the peak electric field at the anode edge of the heterojunction diode such that the observed average breakdown field was higher than 8 MV/cm, achieved for devices with anode to cathode spacing less than 0.2 microns. Control Schottky anode devices (Pt/Al0.58Ga0.42N) fabricated on the same sample displayed an average breakdown field around 4 MV/cm for devices with similar dimensions. While both breakdown fields are significantly higher than those exhibited by incumbent technologies such as GaN-based devices, BaTiO3 can enable more effective utilization of the higher breakdown fields available in ultra-wide bandgap materials by proper electric field management. This demonstration thus lays the groundwork needed to realize ultra-scaled lateral devices with significantly improved breakdown characteristics.
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Vertical $pn$ heterojunction diodes were prepared by plasma-assisted molecular beam epitaxy of unintentionally-doped $p$-type SnO layers with hole concentrations ranging from $p=10^{18}$ to $10^{19}$cm$^{-3}$ on unintentionally-doped $n$-type $beta$-Ga$_{2}$O$_{3}$(-201) substrates with an electron concentration of $n=2.0times10^{17}$cm$^{-3}$. The SnO layers consist of (001)-oriented grains without in-plane expitaxial relation to the substrate. After subsequent contact processing and mesa etching (which drastically reduced the reverse current spreading in the SnO layer and associated high leakage) electrical characterization by current-voltage and capacitance-voltage measurement was performed. The results reveal a type-I band alignment and junction transport by thermionic emission in forward bias. A rectification of $2times10^{8}$ at $pm1$V, an ideality factor of 1.16, differential specific on-resistance of 3.9m$Omegathinspace$cm$^{2}$, and built-in voltage of 0.96V were determined. The $pn$-junction isolation prevented parallel conduction in the highly-conductive Ga$_{2}$O$_{3}$ substrate (sheet resistance $R_{S}approx3thinspaceOmega$) during van-der-Pauw Hall measurements of the SnO layer on top ($R_{S}approx150$k$Omega$, $papprox2.5times10^{18}$cm$^{-3}$, Hall mobility $approx1$cm$^{2}$/Vs). The measured maximum reverse breakdown voltage of the diodes was 66V, corresponding to a peak breakdown field 2.2MV/cm in the Ga$_{2}$O$_{3}$-depletion region. Higher breakdown voltages that are required in high-voltage devices could be achieved by reducing the donor concentration in the $beta$-Ga$_{2}$O$_{3}$ to increase the depletion width as well as improving the contact geometry to reduce field crowding.
We fabricate AlGaN nanowires by molecular beam epitaxy and we investigate their field emission properties by means of an experimental setup using nano-manipulated tungsten tips as electrodes, inside a scanning electron microscope. The tip-shaped anode gives access to local properties and allows collecting electrons emitted from areas as small as 1$mu m^2$. The field emission characteristics are analyzed in the framework of Fowler-Nordheim theory and we find a field enhancement factor as high as $beta$ = 556 and a minimum turn-on field $E_{turn-on}$ = 17 V/$mu$m for a cathode-anode separation distance d = 500 nm. We show that for increasing separation distance, $E_{turn-on}$ increases up to about 35 V/$mu$m and $beta$ decreases to 100 at d = 1600 nm. We also demonstrate the time stability of the field emission current from AlGaN nanowires for several minutes. Finally, we explain the observation of modified slope of the Fowler-Nordheim plots at low fields in terms of non-homogeneous field enhancement factors due to the presence of protruding emitters.
Wide and ultra-wide band gap semiconductors can provide excellent performance due to their high energy band gap, which leads to breakdown electric fields that are more than an order of magnitude higher than conventional silicon electronics. In materials where p-type doping is not available, achieving this high breakdown field in a vertical diode or transistor is very challenging. We propose and demonstrate the use of dielectric heterojunctions that use extreme permittivity materials to achieve high breakdown field in a unipolar device. We demonstrate the integration of a high permittivity material BaTiO3 with n-type $beta$-Ga2O3 to enable 5.7 MV/cm average electric field and 7 MV/cm peak electric field at the device edge, while maintaining forward conduction with relatively low on-resistance and voltage loss. The proposed dielectric heterojunction could enable new design strategies to achieve theoretical device performance limits in wide and ultra-wide band gap semiconductors where bipolar doping is challenging.
Two-dimensional (2D) materials and heterostructures have recently gained wide attention due to potential applications in optoelectronic devices. However, the optical properties of the heterojunction have not been properly characterized due to the limited spatial resolution, requiring nano-optical characterization beyond the diffraction limit. Here, we investigate the lateral monolayer MoS2-WS2 heterostructure using tip-enhanced photoluminescence (TEPL) spectroscopy on a non-metallic substrate with picoscale tip-sample distance control. By placing a plasmonic Au-coated Ag tip at the heterojunction, we observed more than three orders of magnitude photoluminescence (PL) enhancement due to the classical near-field mechanism and charge transfer across the junction. The picoscale precision of the distance-dependent TEPL measurements allowed for investigating the classical and quantum tunneling regimes above and below the ~320 pm tip-sample distance, respectively. Quantum plasmonic effects usually limit the maximum signal enhancement due to the near-field depletion at the tip. We demonstrate a more complex behavior at the 2D lateral heterojunction, where hot electron tunneling leads to the quenching of the PL of MoS2, while simultaneously increasing the PL of WS2. Our simulations show agreement with the experiments, revealing the range of parameters and enhancement factors corresponding to various regimes. The controllable photoresponse of the lateral junction can be used in novel nanodevices.
Single-photon emitting devices have been identified as an important building block for applications in quantum information and quantum communication. They allow to transduce and collect quantum information over a long distance via photons as so called flying qubits. In addition, substrates like silicon carbide provides an excellent material platform for electronic devices. In this work we combine these two features and show that one can drive single photon emitters within a silicon carbide p-i-n-diode. To achieve this, we specifically designed a lateral oriented diode. We find a variety of new color centers emitting non-classical lights in VIS and NIR range. One type of emitter can be electrically excited, demonstrating that silicon carbide can act as an ideal platform for electrically controllable single photon sources.
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