Abstract
Due to the absorption of opaque Si substrates, the luminous efficiency of GaN-based light-emitting diodes (LEDs) on Si substrates is not high. So, in this work, we insert AlN/GaN distributed Bragg reflectors (DBRs) to improve the light output of GaN-based LEDs on Si (111) substrates grown via metal organic chemical vapor deposition (MOCVD). In order to obtain the highest reflectivity of the AlN/GaN DBR stop band, the growth parameters of AlN/GaN DBRs are optimized, including the growth temperature, the V/III ratio and the growth pressure. As a consequence, the interfaces of the optimal 9-pair AlN/GaN DBRs become abrupt, and the reflectivity of the DBR stop band is as high as 85.2%, near to the calculated value (92.5%). Finally, crack-free GaN-based LEDs with 5-pair AlN/GaN DBRs are grown on Si (111) substrates. The light output of the DBR-based LED is evidently enhanced by 41.8% at the injection current of 350 mA, compared with the conventional DBR-based LED without DBRs. These results pave the way for the luminous efficiency improvement of future green and red GaN-based LEDs grown on Si substrates.
Highlights
In the past two decades, III-Nitride distributed Bragg reflectors (DBRs) have been applied in light-emitting diodes (LEDs) to improve the light output [1,2,3,4] or even in vertical-cavity surface-emitting lasers as resonant cavities [5]
Crack-free GaN-based LEDs with 5-pair AlN/GaN DBRs are grown on Si (111)
We insert AlN/GaN DBRs to enhance the light output of GaN-based LEDs on Si
Summary
In the past two decades, III-Nitride DBRs have been applied in LEDs to improve the light output [1,2,3,4] or even in vertical-cavity surface-emitting lasers as resonant cavities [5]. Due to the important advantage in that III-Nitride DBRs can be fabricated by in situ epitaxy, many approaches have been adopted such as AlN/GaN [6,7,8,9,10], AlGaN/GaN [11,12], AlGaN/AlN [13,14,15,16], AlInN/GaN [17,18,19], AlInN/AlGaN [20,21] and so on.
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