skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, December 13 until 2:00 AM ET on Saturday, December 14 due to maintenance. We apologize for the inconvenience.


Search for: All records

Award ID contains: 1916800

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    We investigate the electrical characteristics of Ni Schottky contacts on n-type GaN films that have undergone ultra-high-pressure annealing (UHPA), a key processing step for activating implanted Mg. Contacts deposited on these films exhibit low rectification and high leakage current compared to contacts on as-grown films. By employing an optimized surface treatment to restore the GaN surface following UHPA, we obtain Schottky contacts with a high rectification ratio of ∼109, a near-unity ideality factor of 1.03, and a barrier height of ∼0.9 eV. These characteristics enable the development of GaN junction barrier Schottky diodes employing Mg implantation and UHPA.

     
    more » « less
  2. Abstract

    Recent successful integration of semiconductors into spintronic THz emitters has demonstrated a new pathway of control over terahertz (THz) radiation through ultrafast demagnetization dynamics. Here, the spintronic THz emission from different ultrawide bandgap (UWBG) semiconductors interfaced with ferromagnets is studied. The authors show that the Schottky barrier in the UWBG semiconductor AlN acts as a spin filter that increases the polarization of the spin current injected from the ferromagnet. Furthermore, the authors show that the two‐dimensional electron gas at the interface between Al0.25Ga0.75N and GaN enhances the magnitude of the emitted radiation due to the high spin‐to‐charge conversion efficiency induced by the Rashba effect that results in a hallmark asymmetry in emission amplitude. The results provide a framework for future engineering of semiconducting/ferromagnet heterostructures for ultrafast communications technologies beyond 5G.

     
    more » « less
  3. High p-conductivity (0.7 Ω−1 cm−1) was achieved in high-Al content AlGaN via Mg doping and compositional grading. A clear transition between the valence band and impurity band conduction mechanisms was observed. The transition temperature depended strongly on the compositional gradient and to some degree on the Mg doping level. A model is proposed to explain the role of the polarization field in enhancing the conductivity in Mg-doped graded AlGaN films and the transition between the two conduction types. This study offers a viable path to technologically useful p-conductivity in AlGaN.

     
    more » « less
  4. Highly conductive Ge-doped AlN with conductivity of 0.3 (Ω cm)−1 and electron concentration of 2 × 1018 cm−3 was realized via a non-equilibrium process comprising ion implantation and annealing at a moderate thermal budget. Similar to a previously demonstrated shallow donor state in Si-implanted AlN, Ge implantation also showed a shallow donor behavior in AlN with an ionization energy ∼80 meV. Ge showed a 3× higher conductivity than its Si counterpart for a similar doping level. Photoluminescence spectroscopy indicated that higher conductivity for Ge-doped AlN was achieved primarily due to lower compensation. This is the highest n-type conductivity reported for AlN doped with Ge to date and demonstration of technologically useful conductivity in Ge-doped AlN.

     
    more » « less
  5. Record-low p-type resistivities of 9.7 and 37 Ω cm were achieved in Al0.7Ga0.3N and Al0.8Ga0.2N films, respectively, grown on single-crystal AlN substrate by metalorganic chemical vapor deposition. A two-band conduction model was introduced to explain the anomalous thermal behavior of resistivity and the Hall coefficient. Relatively heavy Mg doping (5 × 1019 cm−3), in conjunction with compensation control, enabled the formation of an impurity band exhibiting a shallow activation energy of ∼30 meV for a wide temperature range. Valence band conduction associated with a large Mg ionization energy was dominant above 500 K. The apparently anomalous results deviating from the classical semiconductor physics were attributed to fundamentally different Hall scattering factors for impurity and valence band conduction. This work demonstrates the utility of impurity band conduction to achieve technologically relevant p-type conductivity in Al-rich AlGaN.

     
    more » « less
  6.  
    more » « less
  7. High room temperature n-type mobility, exceeding 300 cm2/Vs, was demonstrated in Si-doped AlN. Dislocations and CN−1 were identified as the main compensators for AlN grown on sapphire and AlN single crystalline substrates, respectively, limiting the lower doping limit and mobility. Once the dislocation density was reduced by the growth on AlN wafers, C-related compensation could be reduced by controlling the process supersaturation and Fermi level during growth. While the growth on sapphire substrates supported only high doping ([Si] > 5 × 1018 cm−3) and low mobility (∼20 cm2/Vs), growth on AlN with proper compensation management enabled controlled doping at two orders of magnitude lower dopant concentrations. This work is of crucial technological importance because it enables the growth of drift layers for AlN-based power devices.

     
    more » « less
  8.  
    more » « less
  9. Abstract We report a kV class, low ON-resistance, vertical GaN junction barrier Schottky (JBS) diode with selective-area p-regions formed via Mg implantation followed by high-temperature, ultra-high pressure (UHP) post-implantation activation anneal. The JBS has an ideality factor of 1.03, a turn-on voltage of 0.75 V, and a specific differential ON-resistance of 0.6 mΩ·cm 2 . The breakdown voltage of the JBS diode is 915 V, corresponding to a maximum electric field of 3.3 MV cm −1 . These results underline that high-performance GaN JBS can be realized using Mg implantation and high-temperature UHP post-activation anneal. 
    more » « less
  10. A two-band transport model is proposed to explain electrical conduction in graded aluminum gallium nitride layers, where the free hole conduction in the valence band is favored at high temperatures and hopping conduction in the impurity band dominates at low temperatures. The model simultaneously explains the significantly lowered activation energy for p-type conduction (∼10 meV), a nearly constant sheet conductivity at lower temperatures (200–330 K), and the anomalous reversal of the Hall coefficient caused by the negative sign of the Hall scattering factor in the hopping conduction process. A comparison between the uniform and graded samples suggests that compositional grading significantly enhances the probability of phonon-assisted hopping transitions between the Mg atoms.

     
    more » « less