More Like this

1. Improving vertical GaN p-n diode performance with room temperature defect mitigation

   https://doi.org/10.1088/1361-6641/ad10c3  

   Sultan Al-Mamun, Nahid ; Gallagher, James ; Jacobs, Alan ; Hobart, Karl D. ; Anderson, Travis J. ; Gunning, Brendan ; Kaplar, Robert J. ; Wolfe, Douglas E. ; Haque, Aman ( November 2023 , Semiconductor Science and Technology)

   Defect mitigation of electronic devices is conventionally achieved using thermal annealing. To mobilize the defects very high temperature is necessary. Since thermal diffusion is random in nature, the process may take a prolonged period of time. In contrast, we demonstrate a room temperature annealing technique that takes only a few seconds. The fundamental mechanism is defect mobilization by atomic scale mechanical force originated from very high current density but low duty cycle electrical pulses. The high energy electrons lose their momentum upon collision with defects, yet low duty cycle suppresses any heat accumulation to keep the temperature at ambient. For 7×105 A/cm2 pulsed current, we report approximately 26% reduction in specific on-resistance, 50% increase of rectification ratio with lower ideality factor and reverse leakage current for as-fabricated vertical geometry GaN p-n diodes. We characterized microscopic defect density of the devices before and after the room temperature processing to explain the improvement in the electrical characteristics. Raman analysis reveals improvement in crystallinity of the GaN layer and approximately 40% relaxation of any post-fabrication residual strain compared to the as-received sample. Cross-sectional transmission electron microscopy (TEM) images and geometric phase analysis (GPA) results of high-resolution TEM (HRTEM) images further confirm the effectiveness of the proposed room temperature annealing technique to mitigate defects in the device. No detrimental effect, such as diffusion and/or segregation of elements, is observed as a result of applying high density pulsed current, as confirmed by energy dispersive X-ray spectroscopy (EDX) mapping.

    

   more » « less
2. Distributed polarization-doped GaN p–n diodes with near-unity ideality factor and avalanche breakdown voltage of 1.25 kV

   https://doi.org/10.1063/5.0083302  

   Nomoto, Kazuki ; Li, Wenshen ; Song, Bo ; Hu, Zongyang ; Zhu, Mingda ; Qi, Meng ; Protasenko, Vladimir ; Zhang, Zexuan ; Pan, Ming ; Gao, Xiang ; et al ( March 2022 , Applied Physics Letters)

   Polarization-induced (Pi) distributed or bulk doping in GaN, with a zero dopant ionization energy, can reduce temperature or frequency dispersions in impurity-doped p–n junctions caused by the deep-acceptor-nature of Mg, thus offering GaN power devices promising prospects. Before comprehensively assessing the benefits of Pi-doping, ideal junction behaviors and high-voltage capabilities should be confirmed. In this work, we demonstrate near-ideal forward and reverse I–V characteristics in Pi-doped GaN power p–n diodes, which incorporates linearly graded, coherently strained AlGaN layers. Hall measurements show a net increase in the hole concentration of 8.9 × 10¹⁶ cm⁻³in the p-layer as a result of the polarization charge. In the Pi-doped n-layer, a record-low electron concentration of 2.5 × 10¹⁶ cm⁻³is realized due to the gradual grading of Al_0-0.72GaN over 1  μm. The Pi-doped p–n diodes have an ideality factor as low as 1.1 and a 0.10 V higher turn-on voltage than the impurity-doped p–n diodes due to the increase in the bandgap at the junction edge. A differential specific on-resistance of 0.1 mΩ cm²is extracted from the Pi-doped p–n diodes, similar with the impurity-doped counterpart. The Pi-doped diodes show an avalanche breakdown voltage of ∼1.25 kV, indicating a high reverse blocking capability even without an ideal edge-termination. This work confirms that distributed Pi-doping can be incorporated in high-voltage GaN power devices to increase hole concentrations while maintaining excellent junction properties.

    

   more » « less
3. Schottky contacts to N-polar GaN with SiN interlayer for elevated temperature operation

   https://doi.org/10.1063/5.0083588  

   Khachariya, Dolar ; Szymanski, Dennis ; Reddy, Pramod ; Kohn, Erhard ; Sitar, Zlatko ; Collazo, Ramón ; Pavlidis, Spyridon ( April 2022 , Applied Physics Letters)

   In this Letter, we unveil the high-temperature limits of N-polar GaN Schottky contacts enhanced by a low-pressure chemical vapor deposited (LPCVD) SiN interlayer. Compared to conventional Schottky diodes, the insertion of a 5 nm SiN lossy dielectric interlayer in-between Ni and N-polar GaN increases the turn-on voltage ( V ON ) from 0.4 to 0.9 V and the barrier height ( ϕ B ) from 0.4 to 0.8 eV. This modification also reduces the leakage current at zero bias significantly: at room temperature, the leakage current in the conventional Schottky diode is >10 3 larger than that observed in the device with the SiN interlayer, while at 200 °C, this ratio increases to 10 5 . Thus, the rectification ratio (I ON /I OFF ) at ±1.5 V reduces to less than one at 250 °C for the conventional Schottky diode, whereas for SiN-coated diodes, rectification continues until 500 °C. The I–V characteristics of the diode with an SiN interlayer can be recovered after exposure to 400 °C or lower. Contact degradation occurs at 500 °C, although devices are not destroyed yet. Here, we report N-polar GaN Schottky contact operation up to 500 °C using an LPCVD SiN interlayer. 

   more » « less
4. High-density polarization-induced 2D electron gases in N-polar pseudomorphic undoped GaN/Al0.85Ga0.15N heterostructures on single-crystal AlN substrates

   https://doi.org/10.1063/5.0107159  

   Zhang, Zexuan ; Encomendero, Jimy ; Kim, Eungkyun ; Singhal, Jashan ; Cho, YongJin ; Nomoto, Kazuki ; Toita, Masato ; Xing, Huili Grace ; Jena, Debdeep ( August 2022 , Applied Physics Letters)

   The polarization difference and band offset between Al(Ga)N and GaN induce two-dimensional (2D) free carriers in Al(Ga)N/GaN heterojunctions without any chemical doping. A high-density 2D electron gas (2DEG), analogous to the recently discovered 2D hole gas in a metal-polar structure, is predicted in a N-polar pseudomorphic GaN/Al(Ga)N heterostructure on unstrained AlN. We report the observation of such 2DEGs in N-polar undoped pseudomorphic GaN/AlGaN heterostructures on single-crystal AlN substrates by molecular beam epitaxy. With a high electron density of ∼4.3 ×1013/cm2 that maintains down to cryogenic temperatures and a room temperature electron mobility of ∼450 cm2/V s, a sheet resistance as low as ∼320 Ω/◻ is achieved in a structure with an 8 nm GaN layer. These results indicate significant potential of AlN platform for future high-power RF electronics based on N-polar III-nitride high electron mobility transistors.

    

   more » « less
5. Systematic oxygen impurity reduction in smooth N-polar GaN by chemical potential control

   https://doi.org/10.1088/1361-6641/ac3638  

   Szymanski, Dennis ; Wang, Ke ; Kaess, Felix ; Kirste, Ronny ; Mita, Seiji ; Reddy, Pramod ; Sitar, Zlatko ; Collazo, Ramon ( November 2021 , Semiconductor Science and Technology)

   Abstract Process chemical potential control and dislocation reduction were implemented to control oxygen concentration in N-polar GaN layers grown on sapphire substrates via metal organic chemical vapor deposition (MOCVD). As process supersaturation was changed from ∼30 to 3400, the formation energy of the oxygen point defect increased, which resulted in a 25-fold decrease in oxygen incorporation. Reducing dislocations by approximately a factor of 4 (to ∼10 9 cm −3 ) allowed for further reduction of oxygen incorporation to the low-10 17 cm −3 range. Smooth N-polar GaN layers with low oxygen content were achieved by a two-step process, whereas first a 1 µ m thick smooth N-polar layer with high oxygen concentration was grown, followed by low oxygen concentration layer grown at high supersaturation. 

   more » « less