Effect of Zn atom diffusion in the active layer of InGaAlP visible-LED investigated by the Piezoelectric Photothermal Sp
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Effect of Zn atom diffusion in the active layer of InGaAlP visible-LED investigated by the Piezoelectric Photothermal Spectroscopy Ryuji Ohno, Yoshihito Taiji, Shoichro Sato, Atsuhiko Fukuyama*, Shigeru Shigetomi** and, Tetsuo Ikari Department of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan * Department of Applied Physics, Miyazaki University, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan ** Department of Physics, Kurume University, 67 Asahityou, Kurume, Fukuoka 830-0011, Japan
ABSTRACT It has been reported that Zn atoms diffused from the Zn-doped p-InAlP cladding to the active layer in InGaAlP visible-light-emitting diodes cause a degradation of light output efficiency. A doping effect of the Zn atoms was then investigated using a Piezoelectric Photothermal Spectroscopy from a nonradiative transition point of view. The results indicate that the Zn-doping unexpectedly induces a decrease of the nonradiative component of the electron transitions above the band gap of the active layer. The experimental results are explained by considering that Zn doping cause the increase of both shallow and deep acceptor levels at the same time with the different rate for generation.
INTRODUCTION Recently, high-brightness operation from the orange to green region have been obtained for the InGaAlP LEDs using InAlP cladding layers and distributed Bragg reflectors (DBRs) grown by metal organic chemical-vapor deposition (MOCVD) method [1]. But one of the problems in the InGaAlP LEDs is a degradation of light output power, which may be caused by the presence of Zn atoms diffused from Zn-doped InAlP cladding layer during the device manufacturing processes. Since a lifetime of the injected carriers in the active layer decreased with increasing Zn concentrations, the diffused Zn was considered to create a not only shallow acceptor but also deep defect levels at the same time in the InGaAlP active layer [2]. However, details have not been clear yet. For the semiconductors which have such deep levels, nonradiative processes may play an important role for the electron transition mechanisms. However, Photoluminescence methods can’t detect such nonradiative transitions. The great advantage of the Piezoelectric Photothermal Spectroscopy (PPTS) is that it is a direct monitor of the nonradiative recombination processes of photoexcited electrons. Therefore, it is useful to clarify the effect of diffused Zn atoms in InGaAlP active layer from the nonradiative transition point of view. We have already reported [3, 4] that the nonradiative transition in semi-insulating bulk GaAs and in AlGaAs/GaAs heterostructure sample could be clearly understood by this technique. In this paper, we propose here a model for an effect of Zn doping and for an electron transition mechanism through the nonradiative pathways to explain our results. The effect of DBRs is H9.28.1
also taken into account. We conclude that deep defect level generated by the Zn atoms diffusion play an important role fo
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