Three-dimensional hole gas induced by polarization in (0001)-oriented metal-face III-nitride structure

Abstract

Polarization-doping via graded AlGaN layer on N-face (0001¯) GaN has been demonstrated as an inspiring p-type doping method for wide-band-gap nitrides. However, the polarity of III-nitrides grown by metal organic chemical vapor deposition is metal-face typically. In this paper, we show that three-dimensional mobile hole gas induced by polarization can be formed in (0001)-oriented metal-face III-nitride structure. The hole concentration of a Mg-doped AlxGa1−xN layer with graded Al composition from x=0.3 to 0 grown on AlN buffer layer is remarkably enhanced, compared with that of a Mg-doped GaN layer grown under the same conditions. In addition, the hole concentration in the graded AlGaN layer is absence of freezeout as the temperature decreases, indicating that the hole is induced by polarization. This p-type doping method paves a way for achieving high-efficiency in wide-band-gap semiconductor light-emitting devices with p-type doping problem.

Advanced Middle-UV Coherent Optical Sources

“…Both N-face [9,28,29,32] and the conventional metal-face [30,31,33] growth can benefit from compositional grading, producing a flat and smooth valence band profile right up to the edge of the active region to ensure superlative hole injection efficiency. If N-face growth is adopted, one must not only ensure good crystalline quality of the epitaxial layers, but also make Ohmic contact to a wide bandgap p-type layer [31].…”

“…Several articles are cited in Satter et al [3] which report new strategies for reduction of the high activation energy of Mg dopants or the increase of free hole concentration in III-N materials. A technique known as "polarization doping" has been suggested for the improvement of p-type dopant (Mg) ionization efficiency in compositionally graded AlGaN layers through the field ionization of the dopant atoms via the electric field induced by polarization charge [9,[28][29][30][31][32][33]. This appellation is somewhat misleading, as electric fields of sufficient magnitude to ionize deep acceptor atoms would necessarily drive free carriers away from the high-field region, leaving behind only fixed space charge rather than highly conductive material.…”

Enhancing carrier injection in the active region of a 280nm emission wavelength LED using graded hole and electron blocking layers

“…To improve internal quantum efficiency, grading has been used in InGaN/AlInGaN quantum wells (QW) based LEDs [10,11,12] with reported 5-6 times enhancement in radiative recombination. Currently, grading schemes have improved carrier injection [10,13,14], and doping [15] in UV-LEDs emitting around 280nm. To date, UV LEDs were championed by SETI Corporation with record external efficiency of more than 11% at 278nm emission wavelength [16].…”

p-doping-free InGaN/GaN light-emitting diode driven by three-dimensional hole gas

“…1,2 To this end, tremendous efforts have been devoted to improve the LED performance through addressing various issues related to material quality, structure optimization, and device design and fabrication. [3][4][5][6][7][8][9][10][11][12] Among these issues, to date a low p-type doping efficiency remains as a limiting factor, which adversely affects the LED performance. In typical p-type GaN, the resulting hole concentration is low because only $1% of Mg dopants are ionized at room temperature.…”

“…9 Recently, it has been also reported that the hole concentration can be increased through the polarization doping. 10,11 The GaN/Al x Ga 1Àx N heterostructures grown along the polar orientations exhibit strong spontaneous and piezo-electric polarizations. 13 Such strong polarizations can induce electric fields causing significant band bending in the GaN/Al x Ga 1Àx N heterostructures.…”