Position-controlled selective area growth of Ga-polar GaN nanocolumns by molecular beam epitaxy

Abstract

Gallium nitride (GaN) is a binary compound semiconductor which belongs to the group III nitrides (III−N). GaN crystallizes typically in the wurtzite structure and has a direct band gap of 3.4 eV. Other members of the III nitrides are indium nitride (InN) and aluminum nitride (AlN), which likewise are of wurtzite crystal phase. The direct band gaps are 0.7 and 6.2 eV, respectively. The GaN-based ternary alloys In Ga 1− N and Al Ga 1− N theoretically allow to tailor the fundamental band gap from the near infrared (InN) to the far ultraviolet (AlN) parts of the electromagnetic spectrum. No other materials system offers this range of direct band gaps [1] . In fact, GaN-based optoelectronic devices are firmly established in everyday life: Solid-state lighting for illumination applications such as full color displays, automotive headlights and ambient lighting [2] utilize GaN-based light emitting diodes (LEDs). High definition optical data storage devices such as Blu-ray players which operate at a wavelength of 405 nm are based on InGaN laser diodes (LDs).The outstanding properties of the III nitrides in general [1,3] , the possibility to continuously tune the band gap, and especially the high melting temperature and the wide band gap of GaN and AlN, allow to envision a variety of GaN-based (high power) optoelectronic applications. These comprise for example photovoltaics, full visible spectrum LEDs, blue and green LDs for projectors (InGaN), and ultraviolet LDs for photolithography, chemical analysis, and medical, as well as environmental applications (AlGaN) [4,5] .Despite the overwhelming application versatility various problems have to be encountered and overcome to pave the way towards this bright future. One of them is related to the growth direction: The III nitrides are subject to polarization effects which cause internal electric fields. In conventional III−N devices, the growth surface is the polar -plane which is described by the Miller-Bravais indices 0001 . The growth direction perpendicular to this plane is 0001 . For this specific geometry, the built-in electric fields are aligned along the growth direction of the light emitting region, which is detrimental to the performance of these devices. A possibility to circumvent or at least reduce these fields is the growth on nonpolar or semipolar surfaces. The former 1100 -and 1120 -surfaces are perpendicular to the -plane. The latter are identified by { } with nonzero , , indices and 10 :