Swaisi Mohamed, Dörfler Andreas, Katoch Rajesh, Ruediger Andreas
INRS-EMT, 1650 Blvd. Lionel-Boulet, Varennes, Québec, J3X 1S2, Canada.
J Phys Condens Matter. 2020 Jul 8;32(29):295701. doi: 10.1088/1361-648X/ab7f03.
We investigate the phenomenon of pyroelectric luminescence in LiNbO single crystals. This faint emission of light due to temperature-induced changes of permanent polarization is induced by different types of charge carrier recombination, outside and inside the crystal. With decreasing atmospheric pressure, the external discharge mechanism transitions from sparse intense gas discharge pulses at ambient pressure, to frequent faint discharges close to 1 mbar, to a continuous emission which is referred to as smooth pyroelectric luminescence. Our experimental setup exposes the crystal to constant positive and negative temperature changes in the range of 360-450 K under high vacuum while simultaneously measuring the surface charge density and the emitted intensity. A microscopic model of the luminescence allows the description of the time-dependent pyroelectric luminescence, in particular the determination of deep trap potentials that are otherwise inaccessible to thermal ionization. Using this model, we show that the behavior of this emission in LiNbO crystals is consistent with the release of trapped electrons by the Poole-Frenkel effect from a Dirac-well potential, while the commonly assumed coulombic trap shape is in clear disagreement with both the temporal evolution of the emission as well as the magnitude of the electric field obtained in our measurements.
我们研究了铌酸锂（LiNbO）单晶中的热释电发光现象。这种由永久极化的温度诱导变化引起的微弱发光，是由晶体内部和外部不同类型的电荷载流子复合所导致的。随着大气压力的降低，外部放电机制从常压下稀疏的强气体放电脉冲，转变为接近1毫巴时频繁的微弱放电，再到一种被称为平滑热释电发光的连续发射。我们的实验装置在高真空条件下，使晶体在360 - 450 K范围内经历恒定的正负温度变化，同时测量表面电荷密度和发射强度。发光的微观模型能够描述随时间变化的热释电发光，特别是确定那些通过热电离难以获取的深陷阱势。使用这个模型，我们表明铌酸锂晶体中这种发射行为与通过普尔 - 弗伦克尔效应从狄拉克阱势中释放被俘获电子的情况一致，而通常假设的库仑陷阱形状与发射的时间演化以及我们测量中获得的电场大小均明显不符。
