Influence of GaN Material Characteristics on Device Performance for Blue and Ultraviolet Light-Emitting Diodes D.W. MERFELD, 1,2 X.A. CAO, 1 S.F. LEBOEUF, 1 S.D. ARTHUR, 1 J.W. KRETCHMER, 1 and M.P. D’EVELYN 1 1.—GE Global Research Center, Niskayuna, NY 12309. 2.—E-mail: merfeldw@crd.ge.com An analysis of blue and near-ultraviolet (UV) light-emitting diodes (LEDs) and material structures explores the dependence of device performance on mater- ial properties as measured by various analytical techniques. The method used for reducing dislocations in the epitaxial III-N films that is explored here is homoepitaxial growth on commercial hydride vapor-phase epitaxy (HVPE) GaN substrates. Blue and UV LED devices are demonstrated to offer superior performance when grown on GaN substrates as compared to the more conven- tional sapphire substrate. In particular, the optical analysis of the near- UV LEDs on GaN versus ones on sapphire show substantially higher light output over the entire current-injection regime and twice the internal quan- tum efficiency at low forward current. As the wavelength is further decreased to the deep-UV, the performance improvement of the homoepitaxially grown structure as compared to that grown on sapphire is enhanced. Key words: GaN, InGaN, light-emitting diode, homoepitaxy, quantum efficiency Journal of ELECTRONIC MATERIALS, Vol. 33, No. 11, 2004 Regular Issue Paper 1401 (Received March 29, 2004; accepted July 13, 2004) INTRODUCTION Gallium nitride (GaN) material has been the sub- ject of intense research over the last decade because of its unique properties, which are particularly bene- ficial in optoelectronic and high-power microwave ap- plications. Thin-film properties of epitaxially grown GaN and other III-N compounds grown on sapphire or SiC are highly dependent on the interface at the substrate, and commonly, a buffer layer is incorpo- rated into the growth recipe to assist in optimizing the initial island-growth conditions as well as to reduce defects brought on by the lattice and thermal expansion mismatch. 1–3 Current commercial, blue light-emitting diodes (LEDs) have been engineered to exhibit high effi- ciency in spite of the high number of dislocations (10 8 –10 10 cm -2 ) that exist in the material. There is a motivation to drive these LEDs at higher injection currents to provide higher lumens per chip area and meet the aggressive cost targets of the solid- state lighting market. 4 However, even high-quality GaN/InGaN-based blue LEDs when subjected to high-injection current 5 and reverse-bias stresses 6 experience gradual degradation of device perfor- mance. Another concern regarding device degrada- tion is that threading dislocations are expected to be even more of an issue as the wavelength of the LED is driven deeper toward the ultraviolet (UV) and the In concentration is reduced, thus diminish- ing the positive effects of In segregation in the active region. 7 This is particularly a challenge in the development of near-UV LEDs for use in high color rendering index (CRI) lighting systems and deep-UV LEDs for biofluorescence applications. The problems created by defects in the material can be largely overcome by using a high-quality bulk GaN substrate. 8,9 Besides reducing the cause of most defects and strain, the lattice constant and thermal-expansion coefficient mismatch between the epilayers and the substrate, the growth recipe is also simplified because the initial nucleation steps required for growth on sapphire and SiC are not needed. Furthermore, an LED grown on an electri- cally conductive GaN substrate can be designed to operate in a vertical configuration, allowing for a