MME uses metal-rich fluxes, shuttering the metal sources while impingent nitrogen remains constant in order to consume any accumulated metal on the surface. This technique allows for lower substrate temperatures in order to facilitate the growth of high-indium content, non-phase-separated InGaN films. The samples here were grown well within the miscibility gap, from 22% to 67% indium fraction. Key growth considerations will be discussed in details, with a focus on transient RHEED analysis which plays a critical role in optimizing the InGaN growth chemistry. By monitoring the growth surface with RHEED, phase separation can be avoided without sacrificing crystal quality as is traditionally seen for nitrogen-rich growth. The InGaN films grown demonstrate GaN template-limited crystal quality with (0002) rocking curve FWHM less than 420 arcseconds in all cases, as well as smooth surfaces with less than 1nm RMS roughness. Figure 2 shows the XRD spectrum and AFM morphology for one such InGaN film with 67% indium fraction.

MME has also been a highly successful growth method for p-type GaN and InGaN films. Compared to the traditional hole concentrations in GaN of 10¹⁷to 10¹⁸cm^-3, MME has demonstrated hole concentrations of up to 7.9x10¹⁹cm^-3in GaN and 3x10¹⁹cm^-3in InGaN films with up to 15% indium content. Moreover, MME-grown p-type GaN films have shown Mg acceptor activation efficiencies greater than 50%, compared to less than 10% as is traditionally reported. As with the high-indium InGaN films above, transient RHEED analysis is used to facilitate the extremely high Mg acceptor incorporation and activation, for which specific conditions and signatures will be discussed. Temperature-dependent Hall Effect is used to explore the electrical properties of these highly p-type GaN and InGaN films. A moderately-doped p-type GaN sample with a room temperature hole concentration of 3x10¹⁸cm^-3showed significant carrier freeze-out and donor-compensated conductivity at low temperatures. In contrast, a heavily-doped sample with room-temperature hole concentration of 2x10¹⁹cm^-3exhibited minimal carrier freeze-out and remained p-type throughout the measured temperature range, with a hole concentration of 5x10¹⁸at just 82K. Similarly, a heavily-doped InGaN sample with 7% indium fraction and room temperature hole concentration of 3x10¹⁹cm^-3also exhibited little carrier freeze-out with nearly 1x10¹⁹cm^-3hole concentration at 90K. Figure 2 is the temperature-dependent resistivity of these three samples, where the resistivity of the sample with moderate doping (black) exhibited a 150x increase in resistivity at low temperature, compared to just a minor increase for the highly doped GaN (blue) and InGaN (green).

Figure 2.Temperature-dependent of resistivity of a traditional p-type GaN (black) which exhibits carrier freeze-out, compared to the highly-doped p⁺-GaN and p⁺-InGaN grown by MME.

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