Observation and control of the surface kinetics of InGaN for the elimination of phase separation

Abstract

The growth of InGaN alloys via Metal-Modulated Epitaxy has been investigated. Transient reflection high-energy electron diffraction intensities for several modulation schemes during the growth of 20% InGaN were analyzed, and signatures associated with the accumulation, consumption, and segregation of excess metal adlayers were identified. A model for shuttered, metal-rich growth of InGaN was then developed, and a mechanism for indium surface segregation was elucidated. It was found that indium surface segregation only occurs after a threshold of excess metal is accumulated, and a method of quantifying this indium surface segregation onset dose is presented. The onset dose of surface segregation was found to be indium-composition dependent and between 1 and 2 monolayers of excess metal. Below this surface threshold off excess metal, metal-rich growth can occur without indium surface segregation. Since at least 2 monolayers of excess metal will accumulate in the case of metal-rich, unshuttered growth of InGaN at the low temperatures required to suppress thermal and spinodal decomposition, this study reveals that some form of modulation must be employed to maintain this adlayer thickness. These theories were applied in the growth of InGaN with varying compositions using Metal-Modulated Epitaxy. Single-phase, high-quality InGaN films with compositions throughout the miscibility gap with root mean square roughnesses less than 0.8 nm were obtained, demonstrating the feasibility of shuttered, metal-rich InGaN growth.

Simulations, Practical Limitations, and Novel Growth Technology for InGaN-Based Solar Cells

“…In addition to p-type doping, MME has also been applied to the growth of high-indium-content InGaN throughout the miscibility gap [43], [44]. The InGaN films grown at solar-relevant compositions exhibit no phase separation or indium segregation, as shown in Fig.…”

“…5. Indium segregation is prevented by limiting the metal adlayer dose [44]. Lumilog MOCVD-grown GaN templates were used as substrates.…”

Indium incorporation dynamics in N-polar InAlN thin films grown by plasma-assisted molecular beam epitaxy on freestanding GaN substrates

“…Growth conditions were chosen well within the N-rich regime to allow independent Φ In and Φ Al series without crossing the N-richto-metal-rich transition, avoiding potential issues with indium accumulation and indium/aluminum liquid phase segregation [25]. Φ N n was calculated from the growth rate of GaN grown in the Ga-rich regime measured by X-ray diffraction (XRD), and converted to equivalent In 0.18 Al 0.82 N growth rate units using the respective clattice constants for relaxed GaN and coherently strained InAlN.…”

“…In addition, there have been reports of poorly understood compositional changes with respect to supplied indium and aluminum flux (Φ In and Φ Al ) [23,24]. InAlN layers are frequently grown with the total Φ In þ Φ Al approximately equal to the supplied active nitroand is complicated by possible indium accumulation and indium/ aluminum liquid phase segregation [25]. Growth temperatures are generally chosen to be low enough to avoid thermal decomposition of InN: around 500 1C for metal-polar InAlN and 550 1C for Npolar InAlN [4,12,23].…”

Pulsed growth techniques in plasma-assisted molecular beam epitaxy of Al Ga1−N layers with medium Al content (x=0.4–0.6)

“…The first one, the so-called metal modulated epitaxy (MME) is based on consumption of excessive metal during short-term interruption of all metal fluxes at the constant values of activated nitrogen flux and substrate temperature. Initially this technique was developed by Ferro et al [7] for growth of binary AlN layers and then it has been applied to growing the InGaN ternary alloys [8][9][10]. The second one, so-called Droplet Elimination by Thermal Annealing (DETA) initially developed by Terashima et al [11] for the growth of GaN/ AlGaN superlattices proceeds through thermal evaporation of the excessive metal (Ga) at the elevated substrate temperature during full growth interruption by shuttering all the fluxes.…”