6.1 Recombination_微电子专业英语-QQ阅读男生历史网

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6.1 Recombination

The thermodynamic nonequilibrium excess chargescan be present in the semiconductor. They can be created by carrier injectionthrough contacts，an electron beam or the absorption of light with wavelength smaller than the bandgap. 2. They can be created by carrier injectionthrough contacts，an electron beam or the absorption of light with wavelength smaller than the bandgap. 提示：by引导的介宾短语作方式状语，包括三个并列的宾语。 After the external excitation is turned off，the semiconductor will return to the equilibrium state. The relaxation of carriers into energetically lower states（and energy release）is called recombination . The term stems from the electron recombining with the hole created after absorption of a photon. 3. The term stems from the electron recombining with the hole created after absorption of a photon. 提示：stem from表示“出自、起源于”；electron recombining with the hole是动名词作主句的宾语；created after absorption of a photon 是过去分词作定语，修饰hole。 However，there are other recombination mechanisms.

6.1.1 Band to Band Recombination

The band-band recombinationis the relaxation from an electron in the conduction band into the valence band（the empty state there is the hole）. In a direct semiconductor，electrons can make an optical transition between the bottom of the conduction band to the top of the valence band. In an indirect semiconductor，this process is only possible with the assistance of a phonon and is thus much less probable.

Fig.6.1 Processes of band band recombination：（a）spontaneous emission，（b）absorption and（c）stimulated emission. A full（empty）circle represents an occupied（unoccupied）electron state.

Fig.6.1（a）shows the processes of the spontaneous recombinationof an electron of energy Eeand a hole of energy Eh. A similar consideration is made for the absorptionprocess ［Fig.6.1（b）］. An electron is transferred upon light absorption from a valence-band state（occupied）to a conduction-band state that must be empty. The process is proportional to the light intensity.

In stimulated emission，an incoming photon triggers’ the transition of an electron in the conduction band into an empty state in the valence band. The emitted photon is in phase with the initial photon ［Fig.6.1（c）］. 4. The emitted photon is in phase with the initial photon ［Fig.6.1（c）］. 提示：in phase表示“同相地，协调地”。

6.1.2 Free-Exciton Recombination

The observation of free-excitons is limited for semiconductors with a small exciton binding energies（such as in GaAs）to low temperatures. 5. The observation of free-excitons is limited for semiconductors with a small exciton binding energies（such as in GaAs）to low temperatures. 提示：be limited to…表示“被限制于……”，句子在limited和to之间插入了一个介词短语（for…）；如果直译为“对自由激子的观察只能限制在低温下”，显得生硬，翻译时可做适当调整。 However，for large exciton binding energy，recombination from free-excitons is observed even at room temperature，as shown in Fig.6.2 for ZnO.

6.1.3 Auger Recombination

In competition with the radiative，bimolecular recombination is the Auger recombination（Fig.6.3）. 6. In competition with the radiative，bimolecular recombination is the Auger recombination（Fig.6.3）. 提示：句中的词汇意义应与物理过程相结合。radiative指复合中伴有发射过程；bimolecular指复合过程中有双粒子参与；句子采用了倒装的形式，真正的主语为the Auger recombination，In competition with the radiative，bimolecular recombination为表语；In competition with…表示“与……存在竞争关系”，the radiative，bimolecular recombination指前文提到的伴随发射过程的双粒子复合，在翻译时可以根据物理意义做出调整。 In the Auger process，the energy that is released during the recombination of an electron and hole is not emitted with a photon but，instead，transferred to a third particle. This can be an electron ［eeh，Fig.6.3（a）］ or a hole ［hhe，Fig.6.3（b）］. The energy is eventually transferred nonradiatively from the hot third carrier via phonon emission to the lattice. 7. The energy is eventually transferred nonradiatively from the hot third carrier via phonon emission to the lattice. 提示：the hot third carrier的理解应结合上下文，上文提到“在俄歇复合的过程中，电子与空穴复合放出的能量并不以发射一个光子的形式释放，而是将能量转移给第三个粒子”，因此the hot third carrier指上文提到的接受了能量的第三个粒子（具有较高能量的热载流子）；from the hot third carrier、via phonon emission和to the lattice这三个介词短语都作状语，表示能量传递是“从何处”、“通过什么方式”和“到哪里”。 The probability for such process is ∝ n 2p if two electrons are involved and ∝ np 2 if two holes are involved. The Auger process is a three-particle process and becomes likely for high carrier density，either through doping，in the presence of many excess carriers，or in semiconductors with small bandgap. 8. The Auger process is a three-particle process and becomes likely for high carrier density，either through doping，in the presence of many excess carriers，or in semiconductors with small bandgap. 提示：句中is和becomes是并列的系动词，句中的likely是形容词，作becomes的表语，表示“很可能的”。either…or…引导的状语指出俄歇复合容易发生的两种情况。in the presence of many excess carriers是插入语，表示掺杂可能导致的一种容易引起俄歇复合的结果。 Auger recombination is the inverse of the impact ionization .

Fig.6.2 Charge-carrier distribution during inversion，necessary for lasing. Shadedareas are populated with electrons. A stimulated transition between an electron and a hole is indicated.

Fig.6.3 Schematic representation of Auger recombination. An electron recombines with a hole and transfers the energy to（a）another electron in the conduction band，（b）another electron in the valence band.

6.1.4 Band-Impurity Recombination

Another recombination process is the capture of carriers by impurities. This process is in competition with all other recombination processes，e. g. the radiative recombination and the Auger mechanism. 9. This process is in competition with all other recombination processes，e. g. the radiative recombination and the Auger mechanism. 提示：in competition with可表示几种复合机制存在竞争的关系。 The band-impurity recombinationis the inverse process to the carrier release from impurities. It is particularly important at low carrier densities，for high dopant concentration and in indirect semiconductors since for these the bimolecular recombination is slow. The theory of capture on and recombination involving impurities is called Shockley-Read-Hall（SRH）kinetics. 10. The theory of capture on and recombination involving impurities is called Shockley-Read-Hall（SRH）kinetics. 提示：of引导的介宾短语作主语theory的定语，这一介宾短语的宾语包括并列的两部分：capture on impurities（杂质能级上的俘获）和recombination involving impurities（与杂质相关的复合），由于两者中的介宾短语（on impurities和involving impurities）共用宾语impurities，所以前者将其省略。 An example of-band impurity recombination is shown in Fig.6.4

6.1.5 Surface Recombination

A surface is typically a source of recombination，e. g. by midgap levels induced by the break of crystal symmetry. The surface recombinationvelocity for GaAs is shown in Fig.6.5. For InP，if the surface Fermi level is pinned close to midgap，the surface recombination velocity increases from ～ 5 × 103 cm/s for a doping level of n ～ 3×1015 cm-3 to ～ 106 cm/s for a doping level of n ～ 3×1018 cm-3 . For Si，the surface recombination rate depends on the treatment of the surface and lies in the range between 10～104 cm/s . The Si-SiO2 interface can exhibit S ≤ 0.5 cm/s.

Fig.6.4 Band-to-impurity processes at an impurity with one level（left：initial，right：final state in each part）：（a）electron capture（from conduction band），（b）electron emission（into conduction band），（c）hole capture（from valence band），（d）hole emission（into valence band）. The arrows indicate the transition of the electron.

Fig.6.5 Surface recombination velocity for GaAs as a function of n-type doping concentration. Different experimental points correspond to different surface tre atment methods. Dashed line is a guide to the eye.