講演情報
[16p-W9_323-16]窒化ガリウム中の格子間マグネシウムの多重安定性とキャリヤー再結合増速マイグレーション
〇趙 元晟1,2,3、白石 賢二1,4、成田 哲生5、押山 淳1,4 (1.名大IMASS、2.(株)QUEMIX、3.東大院理物理、4.東北大CIES、5.豊田中研)
キーワード：
半導体、拡散、キャリア再結合
We present density-functional-theory calculations which provide a microscopic picture of the recombination-enhanced migration of interstitial Mg in GaN. In addition to conventional doubly positive Mg at octahedral site (MgO2+) and at tetrahedral site, we have found two new metastable interstitial complexes. More interestingly, these metastable geometries are found to capture one or two electrons depending on the EF position and become 1+ or neutral charge states, respectively, opening a possibility of recombination-enhanced/retarded migration of the Mg interstitial, in which the charge state of Mg is varying during migration. We have indeed found that starting from the most stable MgO2+, Mg captures an electron becoming the 1+ charge state and overcomes a barrier of 1.65 eV to migrate to the neighboring O site via one of the metastable geometries, much reduced from 2.23 eV in case of migration with the 2+ charge state kept. Moreover, further electron capture is realized accompanied by substantial structural relaxation, thus Mg becoming neutral. Detailed calculations show that capturing the second electron itself requires 1.55 eV from MgO2+, but Mg can then migrate free from any additional energy barriers, thus clarifying the important role of the carrier recombination for Mg migration in GaN. These findings are corroborated by the current quantitative calculations of recombination rates based on electronic Hamiltonian constructed from our DFT-obtained energy spectrum and the Landau–Zener model. The timescale of the recombination is clarified to be in or under the timescale of the migration itself with typical electron density of 1017 cm−3 or above on conduction band. This clearly indicates that the carrier recombination during migration is highly probable and the enhancement by carrier recombination is expected to be significant.