Comparison of 500nm InGaN/GaN QW Emission Properties Induced by Piezoelectric Field Effect and Phase Separation
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Comparison of 500nm InGaN/GaN QW Emission Properties Induced by Piezoelectric Field Effect and Phase Separation Bong Kee, J.M. Koh1, Euijoon Yoon School of materials science and engineering, Seoul national university, Seoul, Korea. 1 Samsung Electro-mechanics Co. Ltd. Suwon, Korea. ABSTRACT Two kinds of InGaN/GaN single quantum well with emission wavelength of 500nm were obtained by employing piezoelectric effect and phase separation with different growth methods. Their emission properties are studied by measuring temperature and photoexcitation power dependent photoluminescence and electrolluminescence. The 500nm luminescence from the sample obtained by piezoelectric effect shows very weak temperature and excitation power dependent, on the other hand, it shows profound band tail broadening at both high temperature and low excitation power for phase separated sample which mean the strong localized state exist. We observed highly bright spots with longer wavelength then that of matrix in the phase separation sample and we believe that high emission efficiency can be obtained from these indium rich clusters. INTROCUCTION Despite rapid advances in growth technology, high indium high quality InGaN films so that to obtain longer emission wavelength is still difficult to achieve using MOCVD due to the high volatility of indium and low pyrolysis efficiency of ammonia. Two kinds of different radiative recombination mechanisms exist during recombination processes in InGaN/GaN quantum well. One is based on spatial indium fluctuations [1,2,3,4] and the other on piezoelectric fields in the layers [5,6,7]. In the first model, radiative transition occur from the recombination of QW excitons localized at certain potential minima due to composition fluctuation or phase separation. The second model attributes the quantumconfined Stark effect (QCSE) to the presence of a large piezoelectric field in the well caused by the lattice mismatch between InGaN and GaN. Strong piezoelectric field cross the InGaN/GaN quantum well separates electron and hole in the quantum well lead to a strong red-shift of resonance energy and reduced oscillator strength. There are some works [8,9,10] on employing phase separation to control longer InGaN wavelength. Phase separation became very important phenomena for high Indium content and high luminescence efficiency control in InGaN layer. In this work, we obtained 500nm emission wavelength from InGaN/GaN single quantum wells (SQW) by employing both piezoelectric effect and phase separation. Their recombination nature were investigated with temperature and excitation power dependent of Photoluminescence. Results show strong localized state exists in the phase separation sample. Highly bright spots with longer wavelength from electrolluminescence microscopy support this observation. EXPERIMENT InGaN/GaN single quantum wells are grown by EMCORE D-180 rotating disc MOCVD system at temperature of 700oC and reactor pressure of 1atm. The input gas phase indium gallium ratio was fixed at In/In+Ga=0.9 during the al
