TOPICAL COLLECTION: 61ST ELECTRONIC MATERIALS CONFERENCE 2019 Optimization of Digital Growth of Thick N-Polar InGaN by MOCVD SHUBHRA S. PASAYAT , 1,5 CORY LUND, 1 YUSUKE TSUKADA, 1 MASSIMO CATALANO, 2 LUHUA WANG, 3 MOON J. KIM, 3 SHUJI NAKAMURA, 4 STACIA KELLER, 1 and UMESH K. MISHRA 1 1.—Department of Electrical and Computer Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, USA. 2.—Istituto Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Via Monteroni, 73100 Lecce, Italy. 3.—Department of Materials Science and Engineering, University of Texas Dallas, 800 W Campbell Rd, Richardson, TX 75080, USA. 4.—Materials Department, University of California, Santa Barbara, Santa Barbara, CA 93106, USA. 5.—e-mail: shubhra@umail.ucsb.edu Smooth 200 nm thick N-polar InGaN films were grown by metal–organic chemical vapor deposition (MOCVD) on sapphire using a digital approach consisting of a constant In, Ga, and N precursor flow with pulsed injection of H 2 into the N 2 carrier gas. Using this growth scheme, the H 2 injection time was altered and the effect on the morphology and indium incorporation in the films observed. The effect of periodic insertion of additional GaN inter-layers on the surface morphology of the InGaN layers was also studied. Key words: Indium gallium nitride (InGaN), gallium nitride (GaN), nitrogen polar (N-polar), metal-organic chemical vapor deposition (MOCVD), digital InGaN growth INTRODUCTION The (In,Ga)N alloy system is attractive for vari- ous optoelectronic and electronic applications owing to its wide, tunable bandgap spanning 0.7–3.4 eV. Thick InGaN films are especially of interest for a variety of applications such as efficient light absorp- tion in solar cells or as relaxed base layers for InGaN based optoelectronic devices. 1,2 In this work we focus on the growth of N-polar InGaN layers. The reversed polarization direction of the internal fields in the N-polar orientation compared to the Ga- polar orientation 1,3 can be advantageous not only for GaN/AlGaN high electron-mobility transistors (HEMTs), 4–6 but also for (In,Ga)N based light emitters, 7–10 photodetectors, 11,12 solar cells, 13 and tunnel devices. 14–16 However, growing thick, high quality InGaN films while maintaining high film quality remains challenging. This is not only because of the large lattice mismatch between GaN and InN, but also due to the low growth temperatures required for sufficient indium incor- poration into the layers. 17,18 While the morphology of metal organic chemical vapor deposition (MOCVD)—grown metal polar (0001) InGaN films typically deteriorates via V-defect formation, 19–21 thicker MOCVD—grown N-polar (000  1) InGaN films exhibit hexagonal surface defects. 1 In contrast to bulk InGaN layers, in InGaN/GaN MQW struc- tures the defect formation can be mitigated by growing parts of the GaN barrier layer in the presence of hydrogen (H 2 ) in the carrier gas. In the case of N-polar films, H 2 was shown to act as a surfactant enhancing the surface mobility of adsorbed species. 1 In a previous study from our research group, digital growth of thick N-polar InGaN films on relaxed plasma-assisted molecular beam epitaxy (PAMBE) grown InGaN pseudo-sub- strates was explored. 2 The growth process investi- gated in this study took advantage of this surfactant effect by introducing short H 2 pulses during InGaN deposition, resulting in the formation of an InGaN/ (Received September 19, 2019; accepted December 3, 2019; published online December 17, 2019) Journal of ELECTRONIC MATERIALS, Vol. 49, No. 6, 2020 https://doi.org/10.1007/s11664-019-07875-3 Ó 2019 The Minerals, Metals & Materials Society 3450