Achievements and perspectives of GaN based light emitting diodes: A critical review

GaN based high brightness white LEDs have been developed as the future of lightening system. Due to their efficiency and exceptionally long lifetime they are seen as a permanent or semi-permanent lightening solution. LEDs available up to date still have many problems with their long time operation and under moderately stressed conditions. The continuous, high performing and maintenance free long operation lifetime is there to be achieved in the future. A lot of research is going on to achieve these goals. This paper provides a critical review of the state of the art LED technologies, their achievements, limitations and proposed solutions to the issues reported till date.

I. Introduction

The development of solid state lightning is showing a revolutionary impact in almost all the lightning applications due to their high energy efficiency and robustness. The development of highly efficient white light emitting diodes is a technological revolution, everyone was waiting for years, and when it came it has been greeted with open arms. A lot of research is being done in past two decades to improve the efficiency, quality and lifetime of WLEDs(white Light Emitting Diodes), and they became better and better, and now days we can see most of the conventional luminaires are being replaced by the luminaries containing different types of LEDs. From a low power mobile backlight to very high powered flood lamps, all are being illuminated by LEDs. They are cheap, they are efficient and best part they are not fragile. They don't have any glass part in them so they are easy to handle. Since the demand of better performance at reduced energy consumption never ends, there is a continuous race to achieve 100% efficiency i.e. to convert every electron-hole pair in the diode to photon and extract them at minimum voltage. In_xGa_{1_x}N has been a promising candidate for solid state lightening for general lightening purpose, because it provides high energy saving and its eco-friendly since there are reduced CO₂, SO₂ and mercury pollution [1]. SSL (Solid State Lightening) devices are shock and vibration resistant and they have considerably long life-span. The properties of light emitting from SSL sources like spatial distribution, color distribution, color temperature and polarization properties are controllable over specific ranges [2], [3]. This all has been possible due to high brightness nitride based LEDs which was first introduced by Shuji Nakamura in 1994 [4]. Fig. 2.

White light generation methods in leds [7].