Far‐Infrared Active Media Based on Shallow Impurity State Transitions in Silicon
Far‐Infrared Active Media Based on Shallow Impurity State Transitions in Silicon
复制标题
基于硅浅杂质态转变的远红外活性介质
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
V. Shastin
中科院分区：
文献类型：
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作者：
E. Orlova;R.Ch. Zhukavin;S. Pavlov;V. Shastin
提出并分析了光泵浦下硅中浅杂质态反布居数的两种机制，并用一种方法减少了跃迁所需的矩阵元数目。第一种机制是基于Si：Bi2p0态与光学声子的共振相互作用。另一种是基于动量守恒定律对Si：P中2p0态声子辅助驰豫的抑制。在CO_2激光光致电离下，在Si：P中记录到浅施主的自发辐射。自发辐射强度与泵浦辐射强度的关系证实了杂质跃迁放大的可能性。导言。人们对基于硅中浅IMPU态的远红外(FIR)活性介质的兴趣有两个原因。第一个是硅对FIR辐射的低水平晶格吸收。第二是主要弛豫过程沿激发库仑杂质态(1)的级联特性，这使得杂质激发态布居的泵浦效率很高，这对于实现连续激光是很重要的。级联弛豫意味着载流子能量减少较小的跃迁占主导地位，当第一激发态或声子弛豫步骤内的激发态群中的一个被反向填充时，受热的载流子参与放大的几率相当高。另一方面，声子辅助的快速弛豫在晶格温度下容易形成平衡分布，是获得杂质态反布居的主要困难。因此，杂质态的反布居意味着具有阈值性质的过程(与光学声子相互作用、光学泵浦)并且比声学声子辅助过程和俄歇过程更快地形成分布的条件，或者它意味着对于特定的状态后者被抑制的条件。另一个复杂的原因是，杂质跃迁的吸收与可能的放大位于相同的频率区域，因此可以阻止它。因此，放大的可能性取决于电荷载流子在激发杂质态上的非平衡分布的细节。
Two mechanisms of the inverse population of shallow impurity states in silicon under optical pumping have been proposed and analyzed, using a procedure allowing to reduce the number of required matrix elements of transitions. The first mechanism is based on the resonance interaction of the 2p0 state in Si : Bi with optical phonons. The other one is based on the suppression of acous- tic-phonon-assisted relaxation from the 2p0 state in Si : P due to the momentum conservation law. Spontaneous emission was registered from shallow donors in Si : P under photoionization by a CO2 laser. The dependence of the spontaneous emission intensity on the intensity of pumping radiation confirms the possibility of amplification on impurity transitions. Introduction. The interest in far-infrared (FIR) active media based on shallow impu- rity states in silicon is caused by two reasons. The first one is the low level of lattice absorption of FIR radiation in silicon. The second is the cascade character of the main relaxation processes along the excited coulombic impurity states (1), allowing to expect high efficiency of pumping of impurity excited states population, which is important for reaching continuous lasing. Cascade relaxation means that transitions with a small re- duction of carrier energy are predominating, and the probability that a heated carrier takes part in the amplification is rather high when one of the first excited states or the group of excited states within the step of phonon relaxation are inversely populated. On the other hand, the fast acoustical-phonon-assisted relaxation causes the main complication in obtaining the inverse population of impurity states, since it tends to form the equilibrium distribution at lattice temperature. Thus, the inverse population of impurity states implies conditions in which the distribution is formed by processes with threshold character (interaction with optical phonons, optical pumping) and being faster than acoustical-phonon-assisted and Auger processes, or it implies conditions, where the latter are suppressed for particular states. The other complication originates from the fact that absorption for impurity transitions lies in the same frequency region as possi- ble amplification and thus can prevent it. Hence the possibility of amplification depends on the details of nonequilibrium distribution of charge carriers over excited impurity states.