Polarization engineered N-polar Cs-free GaN photocathodes

Marini, Jonathan; Mahaboob, Isra; Rocco, Emma; Bell, L. D.

doi:10.1063/1.5029975

Cited by 23 publications

(17 citation statements)

References 51 publications

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“…The gallium nitride (GaN)-based material system and its ternary and quaternary alloys with aluminum (Al) and indium (In) are widely employed in light emitting diodes (LEDs), photodetectors [1][2][3] , and the next generation of power devices [4][5][6][7] . Due to the lack of inversion symmetry within the III-Nitride wurtzite crystal structure the material exhibits a spontaneous polarization charge along the c-direction.…”

Section: We Report On the Enhanced Incorporation Efficiency Of Magnesmentioning

confidence: 99%

“…The GaN crystal can be grown in the Ga-polar (0001), N-polar (0001), semi-polar or non-polar (1100), (1120) orientation. While the Ga-polar orientation has been most extensively studied, the N-polarity has been shown to enhance hole injection 8 and decrease efficiency droop 9 in LEDs, and increase quantum efficiency 3 .…”

Section: We Report On the Enhanced Incorporation Efficiency Of Magnesmentioning

confidence: 99%

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Hillock assisted p-type enhancement in N-polar GaN:Mg films grown by MOCVD

Rocco

Licata

Mahaboob

et al. 2020

Sci Rep

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We report on the enhanced incorporation efficiency of magnesium dopants into facets of hexagonal hillock structures in N-polar GaN, studied by comparative analysis of GaN:Mg films grown by MOCVD on high and low hillock density GaN template layers. Total magnesium concentration in planar regions surrounding a hillock structure is comparable to that within hillock sidewall facets measured at 1.3 × 1019 cm−3 by atom probe tomography, and clustering of Mg atoms is seen in all regions of the film. Within individual hillock structures a decreased Mg cluster density is observed within hillock structures as opposed to the planar regions surrounding a hillock. Additionally, the Mg cluster radius is decreased within the hillock sidewall. The favorable incorporation of Mg is attributed to Mg dopants incorporating substitutionally for Ga during growth of semi-polar facets of the hillock structures. Enhanced p-type conductivity of GaN:Mg films grown on high hillock density template layers is verified by optical and electrical measurement.

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Section: We Report On the Enhanced Incorporation Efficiency Of Magnesmentioning

confidence: 99%

Section: We Report On the Enhanced Incorporation Efficiency Of Magnesmentioning

confidence: 99%

Hillock assisted p-type enhancement in N-polar GaN:Mg films grown by MOCVD

Rocco

Licata

Mahaboob

et al. 2020

Sci Rep

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“…Initial experiments of N-polar GaN photocathodes, reported by Marini et al did not show the expected improvement in QE predicted by the energy band diagram [45]. For similar p-GaN photocathode structures, the as-grown N-polar device has a measured QE of 2.9% compared to a Gapolar device with 6.25% QE at 6 eV photon energy.…”

Section: A Surface Treatmentsmentioning

confidence: 91%

Overview and Progress Toward High-Efficiency, Air Stable, Cs-Free III-Nitride Photocathode Detectors

et al. 2022

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We review the recent progress to achieve air stable III-nitride photocathodes for applications as photon detectors. High conductivity p-type films are critically important to realize high quantum efficiency (QE) photocathodes with effective negative electron affinity (NEA) and downward surface band bending with narrow surface depletion width. Initial reports of III-nitride photocathodes utilize a Cs-surface activation to achieve effective NEA. To attain air stable, Cs-free photocathodes, novel energy band engineering has been shown using Si delta-doping and an n + -GaN cap on the surface of a Gapolar p-GaN layer. Improvement of QE has been achieved utilizing the N-polarity of III-nitrides due to advantageous depletion and polarization charges at the surface. High QE > 25% has been demonstrated by improvements in p-type conductivity with improved Mg-dopant incorporation in N-polar hillock structures and by control over unintentional impurity incorporation and distribution. Further, the importance of achieving high p-type conductivity films is further shown through reviewing recent simulations of GaN photocathodes with varied band bending and hole concentrations. Through comparison of experimental photoemission with Monte Carlo simulations, band structure parameters such as electron effective mass in the conduction band valleys have been elucidated.

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“…This was followed by activation of the buried p-GaN layer by rapid thermal annealing (RTA) in nitrogen at 900 • C for 90 s. Mg-dopant activation process was performed after mesa formation to enable activation of acceptors by lateral and vertical diffusion [32], [33], [34], [35]. Activated p-GaN films with exposed surface layer having a similar Mg concentration showed hole concentration of 2 × 10 17 cm −3 , mobility of 7 cm 2 /V-s and resistivity of 4.721 -cm [36], [37]. Source, drain and back-gate contacts were formed by electron-beam evaporation of Ti (15 nm) / Al (60 nm) / Mo (35 nm) / Au (80 nm) metal stack.…”

Section: Device Design and Processingmentioning

confidence: 99%

Dynamic Control of AlGaN/GaN HEMT Characteristics by Implementation of a p-GaN Body-Diode-Based Back-Gate

Mahaboob

Yakimov

Hogan

et al. 2019

IEEE J. Electron Devices Soc.

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We report on the implementation of dynamic body-bias technique to improve the performance of AlGaN/GaN high electron mobility transistors (HEMTs) with the successful integration of body-diode. In this configuration, p-GaN body-diode-based back-gate control is used to shift the threshold voltage and dynamically modulate the ON/OFF characteristics of a normally-ON AlGaN/GaN HEMT. A fourth back-gate terminal is connected to the p-GaN layer to control the depletion width of the body-diode, which in turn modulates the 2-D electron gas (2DEG) density. A positive/negative shift in the threshold voltage is measured by increasing/decreasing the depletion width below the channel. A positive back-gate bias application in the ON-state is shown to increase the 2DEG current density resulting in higher ON-current. The application of a negative back-gate bias is shown to be effective in the positive shift of the threshold voltage, in reducing the 2DEG channel current and in increasing the OFF-state break-down voltage. We have experimentally demonstrated enhanced effect of body-diode-based back-gate control in shifting the threshold voltage of a normally-ON HEMT toward normally-OFF mode. The optimum back-gate voltage range which can be applied during both ON and OFF states has been experimentally determined.INDEX TERMS AlGaN/GaN HEMT, dynamic body-biasing, body-diode, back-gate, threshold voltage shift.

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Polarization engineered N-polar Cs-free GaN photocathodes

Cited by 23 publications

References 51 publications

Hillock assisted p-type enhancement in N-polar GaN:Mg films grown by MOCVD

Hillock assisted p-type enhancement in N-polar GaN:Mg films grown by MOCVD

Overview and Progress Toward High-Efficiency, Air Stable, Cs-Free III-Nitride Photocathode Detectors

Dynamic Control of AlGaN/GaN HEMT Characteristics by Implementation of a p-GaN Body-Diode-Based Back-Gate

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