書誌事項
- タイトル別名
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- シュクタイ ゼンゴ ノ ハンドウタイ ニ オケル フジュンブツタイ
- Impurity Energy Band in Nearly Degenerate Semiconductor
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説明
縮退前後の半導体の不純物エネルギー帯の形成過程[6]とデバイス設計[7]にも役立つ立場から,特に状態密度の不純物濃度N依存性に関する見通しのよい理論式を得る.Nが非常に増加した縮退前後の半導体の場合では,実際には不純物分布は不規則であるが,平均的にながめると,その分布は周期性"la"を持っていると近似して考えられる."a"は母体結晶の格子定数,"l"はNだけから決まる定数である.したがって,本結晶内のポテンシャル分布はゆるい平均周期"la"で変調された"a"なる周期性となるため,"ほとんど自由な電子近似法がエネルギー帯の解析に適用できる.この新しいゆるい平均周期性を導入することによって初めて,Nに依存する不純物帯の近似式を得ることができるので,本論文ではこの近似の立場をとる.したがって,衆知の方法により波動関数の(4)式を得,それが存在するために必要な条件から,エネルギー帯を規定する行列式,(11)式を得る.更に,ほとんど自由な電子近似ではa_<12>a_<23>a_<13>^*+a_<13>a_<12>^*a_<23>^*なる量はポテンシャルエネルギーの三乗なる量であるため,ポテンシャルエネルギーの二乗と運動エネルギーとの積の項に比し無視しうるので,(12) [numerical formula] 第1項の行列式,第2項と第3項が,おのおのゼロになる場合を求める.それは,おのおの,母体格子と不純物格子の両者が同時に影響した帯,不純物格子だけによる不純物帯,母体結晶だけからなる帯に対応する.こうして,縮帯前後の半導体を不平均なゆるい周期性のポテンシャルで近似することを提案し,その不純物エネルギー帯を簡略に求めたが,実際的立場からは,たとえば,特にn番目の不純物帯に関し,k=π(n-1/2)/laのEで不純物帯最大状態密度g_<1max>が存在し,最近接不純物イオン間のポテンシャルの重なりがあるときとないときでも,N(=(la)^<-3>)の増大によりg_<1max>とNとの関係は,ほぼNによらず,また,その不純物帯の許容幅は,いずれの場合でも,ほぼ,N^<2/3>にに比例し,したがって,電子の活性化エネルギーはN^<2/3>に比例して減少することがわかる.
Simple theoretical expressions of the state-densities of impurity energy bands in the nearly semiconductor are given at the aim of the fact that the expressions are convenient for the dependency of the state-densities on the impurity concentration, and that available for a design theory of degenerate semiconductor devices. In the case of very much impurity concentration N, the impurity distribution in the crystal is actually at random, but an average distribution may be approximated to the case of very weak periodicity of "la", where "a" is the lattice constant of the mother crystal and "l" is a constant determined only by the N. Then, it is found that the potential distribution in this crystal is of "a" periodicity modulated by the weak average periodicity of "la". Thus, "almost free electron approximation" method can be used in the analysis of the impurity energy bands. In the only case of introducing this new weak average periodicity, simple theoretical formulas of impurity band depending upon the "N" may be obtained. In the case of x direction in a crystal, the potential distribution and the wave function are given as Eq. (1) and (2), respectively. The electron motion is given by E1. (3). According to almost free electron approximation, the wave function can be approximated as Eq. (4). When solve the equation of the electron motion, setting energy zero point as Eq. (7), such a determinant as Eq. (11) characterizing energy bands in this crystal is derived from the condition of the existing wave function (4). Still more, a quantity a_<12>a_<23>a^*_<13>+a_13^*_<12>a_<23>^* is cubic of potential energy, so that this quantity may be neglected compared with the products of kinetic energy and square of potential energies. Thus, we can deduce the determinant (11) to Eq. (12) as follows [numerical formula] Each determinatn in Eq. (12) to be equal to zero is solved. It can be found that the first determinant, second's and third's correspond, respectively, to the energy bands affected by both mother crystal lattice and impurity lattice, the impurity energy band constructed by only impurity lattices and by only mother crystal. Then, in this paper, we propose the approximation to the case of the nearly degenerate semiconductor, in which we assume to exist a weak periodic potential, so that the impurity energy bands may be obtained in simple and available form. For examples, as for the n-th impurity band, the maximum state-density of impurity g_<1max> is located at the energy at k=π(n-1/2)/(la). In both cases that potential distributions between impurity atoms are overlapped even between the nearest neighbor impurity ions and that are not overlapped, as increasign N(=(la)^<-3>), g_<1max> is hardly dependent of N and the allowed energy band width almost corresponds to N^<2/3>, so that it may be supposed that an electron activation energy in this nearly degenerate semiconductor decreases with N^<2/3> as increasing N.
資料番号: SA0125068000
収録刊行物
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- 東京大学宇宙航空研究所報告
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東京大学宇宙航空研究所報告 4 (2), 237-252, 1968-04
東京大学宇宙航空研究所
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詳細情報 詳細情報について
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- CRID
- 1050848249891379584
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- NII論文ID
- 110000196934
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- NII書誌ID
- AN00161914
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- ISSN
- 05638100
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- NDL書誌ID
- 8330126
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- 本文言語コード
- ja
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- departmental bulletin paper
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- IRDB
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