Evaluation of Multilayer Structure by Using new High Sensitivity PAS

我们开发了一个使用透明换能器的PAS（光声光谱）。可以定量地评价半导体的吸收系数并进行可重复的实验。由于光可以通过透明换能器照射，产生的声信号被该换能器直接检测到。因此，灵敏度大大提高，没有样品几何限制。特别是对样品的表面层、离子注入层、异质外延层的界面等进行了有效的评价。它非常灵敏，可以探测到离子注入层发出的信号。由于该层非常薄（900-3200,*），因此该方法也适用于评估半导体的表面损伤。在低能区，我们可以检测到离子注入层局域态产生的微弱吸收。通过估算该值，可以定量评价热退火后离子注入层的恢复过程。其次，观察了GaInP/GaAs异质结构和半导体多层结构的PA信号，得到了以下结果：多层结构的每个吸收边分别由PA倾角和大相移确定。在GaInP/GaAs界面上可以清晰地检测到非辐射缺陷。随着辐照波长的变化，当信号源从一层移动到另一层时，在界面层发生PA倾角。这是因为换能器同时检测到每层具有不同幅度的两个不同相位信号。现在我们正试图将信号从压电效应和压电效应中分离出来，并通过与理论分析的比较来定量地评估光学和热常数。

We developed a PAS (Photoacoustic Spectroscopy) using a transparent transducer. It is possible to evaluate an absorption coefficient of semiconductors quantitatively and to perform a reproducible experiment. As the light can irradiate through a transparent transducer, a generated acoustic slignal is directly detected by this transducer. Consequently, the sensitivity is considerably improved and there are no sample geometry limitations. Especially, this method is effective to evaluate the surface layer of the samples, ion implanted layers, interface of heteroepitaxial layers, and so on.1. It is so sensitive that it is possible to detect the signals from the ion implanted layer. As this layer is so thin (900-3200, *) that this method is also applicable to evaluate the surface damages of semiconductors.2. At low energy region we could detect a weak absorption which is generated by the localized states of ion implanted layer. By estimating this value, it is possible to evaluate the recovery process of the thin ion implanted layer by thermal annealing, quantitatively.Next, PA signals from GaInP/GaAs heterostructure and multilayer structures of semiconductors were observed and the following results were obtained.3. Each absorption edge of multilayer structure is determined separately by the PA dips and large phase shift.4. Nonradiative defects are detected clearly at GaInP/GaAs interface.5. The PA dip occurs at interfacial layer when the signal origin moves from one to another layer as irradiated wavelength changes. This is because the transducer detects two different phase signals with different amplitudes of each layer at the same time.6. Now we are trying to separate the signals from piezoelectric and piroelectric effects and to make it possible to evaluate the optical and thermal constants quantitatively by comparing with the theoretical analysis.