Progress in efficient doping of high aluminum-containing group III-nitrides

Abstract

The group III-nitride (InN, GaN, and AlN) class of semiconductors has become one of two that are critical to a number of technologies in modern life—the other being silicon. Light-emitting diodes made from (In,Ga)N, for example, dominate recent innovations in general illumination and signaling. Even though the (In,Ga)N materials system is fairly well established and widely used in advanced devices, challenges continue to impede development of devices that include aluminum-containing nitride films such as (Al,Ga)N. The main difficulty is efficient doping of films with aluminum-rich compositions; the problem is particularly severe for p-type doping, which is essential for Ohmic contacts to bipolar device structures. This review briefly summarizes the fundamental issues related to p-type doping, and then discusses a number of approaches that are being pursued to resolve the doping problem or for circumventing the need for p-type doping. Finally, we discuss an approach to doping under liquid-metal-enabled growth by molecular beam epitaxy. Recent results from a number of groups appear to indicate that p-type doping of nitride films under liquid-metal-enabled growth conditions might offer a solution to the doping problem—at least for materials grown by molecular beam epitaxy.

Enhanced Performance of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes with Chirped Superlattice Electron Deceleration Layer

“…Generally, deficient IQE is caused by large density of defects and threading dislocations, while insufficient LEE is due to the polarization of AlGaN materials and the absorption by the nontransparent p-GaN contact layer [14–18]. Furthermore, electron overflow is the main reason for the poor CIE, which is on account of the inadequate hole density and the significantly imbalanced mobility of electron and hole in AlGaN materials [19, 20].…”

III-Nitride Short Period Superlattices for Deep UV Light Emitters

“…Unfortunately, for III-Ns compounds and their alloys, there is only one convenient p-type dopant, Mg, the experimentally determined activation energy of which varies from ~120 to ~220 meV in GaN [93,94], and reaches more than 500 meV in AlN [94,95]. A detailed analysis of the Mg activation energy in p-AlGaN epitaxial layers over the entire composition range was recently published [96]. It should be noted that if Mg-doped AlGa(In)N is grown using MOCVD, then Mg activation is required.…”

High doping efficiency in p-type Al-rich AlGaN by modifying the Mg doping planes

“…[4][5][6][7][8] However, achieving efficient p-type doping in Al-rich AlGaN is still a great challenge for the following reasons: (i) the limited solubility of magnesium (Mg), which is caused by the high formation enthalpies of Mg substitution for Ga or Al; (ii) the high activation energy for Mg-doped Al x Ga 1Àx N increasing from B170 to 630 meV for x = 0 to x = 1, due to the low valence band maximum, the deep impurity levels, and the heavy effective mass of the holes; and (iii) the strong self-compensation arising from the presence of donor-like native defects and/or complexes. 9 These factors have led to the fact that the doping efficiency of the p-type Al-rich AlGaN reported in most literature is usually less than or around 1%. 5,10,11 So far, a number of p-type doping approaches, including superlattice (SL) doping, 12 Mg delta (d) doping, 13 polarizationinduced hole doping, 7 and Mg-Si alternative co-doping, 14 have been developed to improve the p-type doping efficiency of Al-rich AlGaN.…”