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High Temperature MOCVD grown AlGaN\AlN epilayers


By
Hamad S. Alotaibi

December 26, 2016 - Posted in Discussion
AlGaN material has been demonstrated as a promising candidate for UV devices. High-quality AlGaN is preferably grown on AlN\sapphire buffer layer over GaN\sapphire. AlGaN\GaN will suffer from a biaxial strain after exceeding a critical thickness due to the lattice mismatch between the AlGaN and GaN, especially with high Al composition [1]. Also, GaN template is not recommended for UV devices due to its high absorption of UV light.

However, high-quality AlN is hardly achievable compared to GaN due to its inherent properties. Al adatoms are bigger than Ga adatoms, less mobile, and have higher sticking coefficient. This means that they will not go to the points of impacts on the surface during the growth and will tend to form islands to nucleate. Hence, forming defects will occur when these islands tend to coalesce from different nucleation sites coalesce, which will highly impact the performance of the devices [2]. Low electrical conductivity and surface roughness present a challenge against UV device development efforts.

Many reports have demonstrated high quality AlGaN\AlN by optimizing the growth condition and techniques such as ELO [3] and low temperature buffer layer, but at high Al composition, the quality will deteriorate [4].

High temperature MOCVD growth of AlN is an effective technique to increase the mobility of AlN, which will tempt Al adatoms to be 2-D deposited and consequently reduces the surface roughness and defects. The edge dislocation density is reported to be 4.7×10^8 cm^-2at 1200 C for AlGaN with 80.2% Al composition [5]. Also, as the growth temperature increases, the compressive strain for the AlGaN layers will reduce as shown in figure 1 [1].
 
Hamad 1.png 
Figure 1:  Effect of AlN interlayer growth temperature on strain of AlGaN (NH3 flow 5 slm, 30 nm interlayer thickness).
 
At KAUST, we aim to reach high quality AlN template with a dislocation density of the same magnitude of 10^6  cm^-2 by designing an innovative Extremely-High-Temperature MOCVD reactor which will see the light soon.
Hopefully, this will replace the costly AlN powder templates grown by physical vapor transport that includes high amount UV light absorbing carbon.

 
References
1. McAleese C, Kappers M J, Rayment F D G, et al. Strain effects of AlN interlayers for MOVPE growth of crack-free AlGaN and AlN/GaN multilayers on GaN. J Cryst Growth, 2004, 272(1–4): 475
2. Khan M A, Shatalov M, Maruska H P, et al. III-nitride UV devices. Jpn J Appl Phys, 2005, 44(10): 7179
3. M Imuraa, K Nakanoa, G Naritaa, N Fujimotoa, N Okadaa, K Balakrishnana, M Iwayaa, S Kamiyamaa, H Amanoa, I Akasakia, T Norob, T Takagib, A Bandohc, Epitaxial lateral overgrowth of AlN on trench-patterned AlN layers. J Cryst Growth, 298 (2007) 257–260
4. Kamiyama S, Iwaya M, Hayashi N, et al. Low-temperature deposited AlGaN interlayer for improvement of AlGaN/Ga
5. Y. Jianchang, W. Junxi, L. Naixin, L. Zhe, R. Jun, and L. Jinmin, J. Semicond. 30, 103001 (2009).
 
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2 Comments
Anonymous
February 11, 2017 at 2:27 AM
ASSALALMOU ALAYKOUM WA RAHMATOULLAHI WA BARAKATOUHOU, Dear Dr.Hamad, I am dr.Magdy hussein Mourad, Assistant Professor at Cairo university , national Institute of Laser , specialized on growth and fabrication of III-V semiconductor devices using mocvd and plasma assisted mbe . pls check my link below of the university http://scholar.cu.edu.eg/?q=magdy_mourad/publications i am in cairo my mobile number is : 00201092866917 i was too happy to know that there is an Arabic researcher who is sharing this knowledge as well , please kindly send me your mobile number or how to contact you, waiting to get your mobile number , i carry many research to share with you . ASSALALMOU ALAYKOUM WA RAHMATOULLAHI WA BARAKATOUHOU,
Anonymous
February 11, 2017 at 2:27 AM
ASSALALMOU ALAYKOUM WA RAHMATOULLAHI WA BARAKATOUHOU, Dear Dr.Hamad, I am dr.Magdy hussein Mourad, Assistant Professor at Cairo university , national Institute of Laser , specialized on growth and fabrication of III-V semiconductor devices using mocvd and plasma assisted mbe . pls check my link below of the university http://scholar.cu.edu.eg/?q=magdy_mourad/publications i am in cairo my mobile number is : 00201092866917 i was too happy to know that there is an Arabic researcher who is sharing this knowledge as well , please kindly send me your mobile number or how to contact you, waiting to get your mobile number , i carry many research to share with you . ASSALALMOU ALAYKOUM WA RAHMATOULLAHI WA BARAKATOUHOU,