Comparative Analysis of Defects in Mg-Implanted and Mg-Doped GaN Layers on Freestanding GaN Substrates

Abstract

Inefficient Mg-induced p-type doping has been remained a major obstacle in the development of GaN-based electronic devices for solid-state lighting and power applications. This study reports comparative structural analysis of defects in GaN layers on freestanding GaN substrates where Mg incorporation is carried out via two approaches: ion implantation and epitaxial doping. Scanning transmission electron microscopy revealed the existence of pyramidal and line defects only in Mg-implanted sample whereas Mg-doped sample did not show presence of these defects which suggests that nature of defects depends upon incorporation method. From secondary ion mass spectrometry, a direct correspondence is observed between Mg concentrations and location and type of these defects. Our investigations suggest that these pyramidal and line defects are Mg-rich species and their formation may lead to reduced free hole densities which is still a major concern for p-GaN-based material and devices. As freestanding GaN substrates offer a platform for realization of p-n junction-based vertical devices, comparative structural investigation of defects originated due to different Mg incorporation processes in GaN layers on such substrates is likely to give more insight towards understanding Mg self-compensation mechanisms and then optimizing Mg doping and/or implantation process for the advancement of GaN-based device technology.

Influence of implanted Mg concentration on defects and Mg distribution in GaN

“…[12][13][14] Attempts have been made to understand the formation of such defects and their atomic structures in Mg-doped GaN layers, where Mg is incorporated during GaN growth via metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). 12, [15][16][17][18] However, versatile designing and processing of GaN-based modern devices requires selective-area doping to achieve precise local control over p-type conduction. In a typical GaN-based power device, the high-doped p-type regions are needed as contacts and hole transport layers, while the low-doped regions are needed for inversion channels.…”

Mg diffusion and activation along threading dislocations in GaN

“…[17][18][19][20][21] However, the thermal treatment also induces Mg diffusion and segregation. 22,23 In order to achieve reasonable p-type conductivity with free hole concentrations up to 10 18 cm À3 , a large dosage of Mg implantation is required. However, when the Mg concentration is around 10 19 cm À3 or more, the p-type conductivity is unexpectedly suppressed.…”

“…The depth scale is shown by the left axis. In the Mg-imp layer, both DAP and NBE emissions are weak because nonradiative centers such as vacancy-type defects and Mg-clusters are formed by the Mg implantation of 10 19 cm À3 and subsequent annealing at 1300 C. 23,25 Under the Mg-imp layer, a bright zone exists in the DAP image due to less implantation damage and few nonradiative defects. 29 The high intensity of DAP emission suggests that the ratio of Mg activated as acceptors to nonradiative defects is high in this Mg-activation layer (Mg-act), where the depth is around 700 nm.…”

First‐Principles Study of the Effects of Interstitial H and Point Vacancies on the p‐Type of Conductive Properties of Be/Mg/Ca‐Doped GaN

“…The critical concentration (degeneracy) of the Mott phase transition of GaN semiconductors is reported in the literature. [ 47,48 ] Although GaN materials have various types of shallow donor impurities and are extremely complex, their average effects can be described by a hydrogen‐like model. The radius of electrons in the impurity center was .…”

“…The Bohr radius of the hydrogen atom was 0.53 × 10 −10 m. The effective mass of the electron m was 0.22. When the electron wave function radius was about 4a, that is, the carrier concentration was n ≈ 1/(4a) 3 ≈ 10 18 cm −3 , [ 47,48 ] the conductance transitioned to semimetallization. In this study, the bulk concentrations of the Ga 34 MgN 36 , Ga 34 MgH i N 36 , Ga 34 BeN 36 , Ga 34 BeH i N 36 , Ga 34 CaN 36 , Ga 34 CaH i N 36 , Ga 35 BeN 36 , Ga 35 MgN 36 , and Ga 35 CaN 36 doping systems were 2.33, 3.50, 2.34, 3.51, 2.30, 3.44, 1.17, 1.16, and 1.15 × 10 21 cm −3 , respectively, in the G → F direction.…”