InAsN Grown by Plasma-Assisted Gas Source MBE
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InAsN Grown by Plasma-Assisted Gas Source MBE Ding-Kang Shih, Hao-Hsiung Lin, and Tso-Yu Chu, National Taiwan University, Dept. of Electrical Engineering, Taipei, Taiwan, R.O.C. T. R. Yang, National Taiwan Normal University, Dept. of Physics, Taipei, Taiwan, R.O.C. ABSTRACT We report the structural, electrical and optical properties of bulk InAsN alloy with various nitrogen contents deposited on (100) InP substrates by using plasma-assisted gas source molecular beam epitaxy. It is found that the fundamental absorption edge of InAsN, as compared to that of InAs, shifts to higher energy due to Burstein-Moss effect. A dramatic increase of the electron effective mass in a nitrogen-containing III-V alloy is also observed from infrared reflectivity and Hall measurement on these degenerate InAsN samples. The sizeable increase on electron effective mass is consistent with the theoretical predictions based on band-anticrossing model. INTRODUCTION Group III-V-nitride alloys have a very large band-gap bowing due to the large valence electron energy of the nitrogen atom when compared to other group V atoms [1]. Over the last few years, there have been numerous attempts to explain the large band gap reductions properties of the III-V-N alloys. It has been demonstrated recently that a band anticrossing (BAC) model in which localized N states interact with the extended states of the conduction band can explain the unusual properties of the III-V-N alloys [2]. The huge bowing effect on the band gap energy makes InAsN alloy a promising material for infrared applications. However, only very limited efforts were put on this materials. In this report, we have investigated a series of unintentionally doped InAsN bulk layers with various N contents grown on InP substrates by using gas source molecular beam epitaxy (GSMBE). We found that these samples are with high residual carrier concentration, which increases as N composition increases. Furthermore, the fundamental absorption edge of InAsN, as compared to that of InAs, shifts to higher energy due to the Burstein-Moss (BM) effect [3]. To deduce the ‘real’ band gap energy of our InAsN samples, the energy shift due to BM effect and the band gap narrowing (BGN) effect are considered by using a self-consistent approach based on the BAC model. After the correction, the ‘real’ band gap energy of InAsN samples decreases as N increases, and follows the bowing effect normally. In addition, we found a dramatic increase of the electron effective mass in these InAsN alloys, which is consistent with the theoretical predictions based on BAC model. EXPERIMENTAL DETAILS The InAsN epitaxial layers were grown on semi-insulating InP substrates using GSMBE with RF plasma source as the nitrogen source. Layers were grown at 460°C at a growth rate of 1.5 µm/hr. The ranges of RF power and nitrogen flow rate were from 300W to 480W and from 0.5 to 1.9 sccm, respectively. Detailed growth conditions has been described elsewhere [4]. The thickness of InAsN epitaxial layer was 2µm and the nitrogen composition of the
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