InGaN/GaN multi‐quantum dot light‐emitting diodes

Abstract

It has been demonstrated that InGaN/GaN blue light-emitting diodes (LEDs) with multiple quantum dot (MQD) were successfully fabricated by metal-organic chemical vapor deposition (MOCVD). We have formed nanoscale InGaN self-assembled QDs in the well layers of the active region with a typical 3-nm height and 10-nm lateral dimension. With a 20-mA DC injection current, the forward voltage was 3.1 V and 3.5 V for MQD LED and conventional nitride-based multi-quantum well (MQW) LED with the same structure, respectively. It was also found that EL peak position of the MQD LED is more sensitive to the amount of injection current, as compared to the conventional MQW LEDs.1 Introduction Heteroepitaxial growth of highly strained material systems has been quite attractive as it offers the possibility of producing low-dimensional carrier confinement nanostructures, such as quantum wells (QWs) and quantum dots (QDs) [1]. They present the utmost challenge to semiconductor technology, making possible fascinating novel devices. III-nitride semiconductor materials have a wurtzite crystal structure and a direct energy band gap. We could also achieve nitride-based heteroepitaxial growth easily. At room temperature, the band gap energy of AlInGaN varies from 0.7 to 6.2 eV depends on its composition. Therefore, III-nitride semiconductors are particularly useful for light-emitting diodes (LEDs) and laser diodes (LDs) in this wavelength region [2][3][4][5]. Typical high-brightness LEDs have a multiple quantum well (MQW) active region. The MQW LED is a kind of heterojunction device, in which electrons and holes are confined in the well layers. Thus, one can achieve high quantum efficiency from the MQW LEDs since carrier can recombine easily in the confined well layers [6][7][8][9]. Although high brightness InGaN-GaN MQW LEDs are already commercially available, it can be theoretically predicted that the realization of LEDs with QDs in the active layer would improve the performance of LEDs.Recently, it has been shown that nitride nanostructures can be self-assembled using the strain-induced Stranski-Krastanov (S-K) growth mode without any substrate patterning process [10][11][12]. It has also been shown that nitride nanostructures can be self-assembled using growth interruption during the metalorganic chemical vapor deposition (MOCVD) growth [13]. Although the size fluctuations of selfassembled QDs could result in inhomogeneous optical and electrical characteristics, the self-assembly of strain-induced islands provides the means for creating zero-dimensional quantum structures without having to overcome the current limitations of lithography. These self-assembled QDs could also be used to study novel device physics [14][15][16]. In this work, we report the successful fabrication of blue LEDs with multiple InGaN dots-in-a-well (DWELL) structure, i.e. InGaN-GaN multiple quantum dot (MQD) LEDs, grown on 2-inch sapphire substrates using a growth interruption method in MOCVD system. Details for the formation of QDs are reported in this study. In ...