宁永强半导体材料讲稿第六章 IIIV半导体激光PPT课件

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载流子与光学约束:如双异质结激光所示， 由于双异质结势垒而使载流子在有源区 的两端都被约束住，而同质结激光的载 流子则可离开发生辐射性复合的有源区。 在双异质结激光中，由于有源区内外折 射率差别光被限制在有源区内
一个三层介质的波导，其折射率分别为 n1,n2和n3，其中有源层如三明治般被夹 在两个约束层之间。
在n2>n1>n3的条件下，第一层和第二层 界面的光线角度θ12超过临界角。而第二 层和第三层界面间的θ23也有相似的情况 发生。
因此当有源层的折射率大于周围的折射 率时，光学辐射就被导引(约束)在与各 层界面平行的方向上。
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半导体双异质结对电子、光子限制
Conduction band edge
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6.1 半导体激光器基本原理
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激光器工作的三要素 增益放大介质
粒子数反转 光反馈谐振腔
驻波振荡 阈值条件
腔增益=损耗
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半导体能带和p-n结复合-发光： ：
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半导体激光工作原理 简并型半导体间形成的p-n结或异
质结,这表示在结两端的掺杂能级 甚高，以致于在p型区的费米能级 EFV比价带的边缘还低，而在n型区 的费米能级EFC则高于导带的边缘。 当外加一足够大的偏压时，会产生 大注入的情况，亦即会有很高浓度 的电子与空穴注入转移。 结果在结区域中，导带有大量的电 子而价带则拥有大量的空穴，这就 是分布反转所需的条件。
Eg2
Eg1
Valence band edge
z
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法布里-波罗腔被广 泛地应用在近代的 半导体激光器中。
沿着垂直于＜110＞ 轴的方向劈成一对 平行面，外加适当 的偏压条件时，激 光就能从这些平面 发射出来
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18Biblioteka 19Using a quantum well as active region has several advantages: First, since the band gap increases outside the quantum well (QW), only the QW-region has
to be pumped to generate inversion. Since this volume is very small, the injection current density is reduced by about three orders of magnitude in comparison to homo-junction lasers. Second, the carriers are efficiently captured by the QW’s barrier making it unnecessary to dope the regions close to the junction. The efficiency of radiative recombination reaches more than 90% in modern standard devices, material of highest quality allows for efficiencies of nearly 100%. On the other hand, the low doping results in laser structures with very low internal loss. As a consequence, QW’s opened a way to long lasers of high external efficiency. The reduction of thermal and series resistance by lengthening the lasers up to 4mm for single emitters and 2mm for bars allows the high power of about 4W of 100μm stripe-single emitters and more than 50Wof laser bars, respectively. Third, the quantum well is a layer of about 10-nm thickness. Such thin layers allow for material compositions with lattice constant not fully matching that of GaAs. By replacing gallium partly (typically a few percent) with indium, the addressable wavelength range can be extended up to 1,100 nm. The introduced strain improves the distribution of density of states further and allows threshold current densities of typically 200A/cm2 for high-power semiconductor lasers. By replacing Arsenic with Phosphorous, the wavelength range can be extended down to 730 nm.
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Laser waveguides
Vertical confinement Lateral confinement
第五章 III-V族半导体激光
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整体概况
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6.1 半导体激光器基本原理 6.2 III-V族激光材料 6.3 半导体激光器工艺 6.4 当前的产业情况