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Indium surface segregation in InGaN/GaN quantum wells

A. Dussaigne, B. Damilanoa), N. Grandjean, and J. Massies

Centre National de la Recherche Scientifque Centre de Recherche sur I'HitireEpitaxie et ses Applications Rue B. Grigoq Sophia Antipolis, 06560 Vaibonne, France

' Picogiga, Place Marcel Rebuffat, 91971 Courtaboeuf 7 cedex , France

InGaN/GaN quantum wells (QWs) are very efficient visible light emitters in the blue-green wavelength mge. However, the extemal quantum efficiency of InGaN based light emitting diodes (LEDs) decreases at longer wavelengths [l]. This is mainly due to the presence of a very large piezoelectric field that strongly reduces the oscillator strength via a giant quantum confined Stark effect (QCSE). Another consequence of this QCSE is to increase the sensitivity of the electron and hole wave functions to the interface potential profiles.

Indium surface sepgation phenomenon is well-known to blue-shill the transition energy of I n W C M s QWs by modifying the shape of the potential profile. In the present paper, we investigate both experimentally and theoretically the intluence of In suface sepgahon on InGaN/GaN QW Properties. QW structures were grown by molecular beam epitaxy using N H 3 as nihngen p m r . The growth process is followed in situ by reflection high energy electmn difhchon (RHEED). Figure 1 displays RHEED intensity osclllafions recorded dmkg the growth of InGaN on GaN. Due to specific growth kinetics, these data allow the m m m e n t of the In i n c o p d o n and the determination of the In surface segregation profile.

Transition &ergieS of InGaN/GaN QWs have been modeled wing envelope function formalism. The results of the calculations indicate that the QW energies are blueshifted compared to those of nominal QWs, i.e. without In surface segregation (Figure 2). More interesting for optoelectronic device applicatiom, the oscillator stmgfh is also reduced by In surface segregation (Figure 2). Therefore, with the aim of increasing the wavelength of hi& brightness Inca" QW based LEDs, it is important to reduce as much as possible this effect. Sixategies have then been examined to impmve the radiative efficiency of longwavelength emitting InGaN/GaN QWs.

[l] T. Mukai, S. Nagahama, N. Iwasa, M. Senoh, and T. Yamada, J. Phys. : Condens. Matter. 13, 7089 (2001)

0-7803-7581-5/02/517.00 02002 IEEE 151

i TW=550"C

InGaN i GaN

- . . . I . I . I . I . ' I . I . I .

0 20 40 60 80 100 120 1 Growth Time (s)

io

Fig 1: MEED specular beam intensity oscillations recorded during the growth of InGaN and GaN.

z - x

P c 0) -I a

I I . I . I . I . I . , I l V 3 0.0 0.2 0.4 0.6 0.8 1.0

Segregation coefficient

Fig. 2: Effect of the In surface segregation phenomenon on the transition energy and oscillator strength of I&,2GaosN/GaN quantum wells (calculated).

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