Optimization of Ga(In)NAs thin film growth by atomic hydrogen-assisted molecular beam epitaxy
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0891-EE10-32.1
Optimization of Ga(In)NAs thin film growth by atomic hydrogen-assisted molecular beam epitaxy Yukiko Shimizu, Naoya Miyashita, and Yoshitaka Okada Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan ABSTRACT The effect of growth temperature on the crystal quality and optical properties of Ga(In)NAs films was investigated over a range of 340 ~ 520 °C. We found that Ga(In)NAs films fabricated at lower growth temperatures generally result in an improved crystal quality. An XRD linewidth of as low as 45 arcsec was obtained for a 1 µm-thick Ga0.94In0.06N0.01As0.99 thin film grown at 380 °C. This is ~1/2 of that grown at the conventionally-adopted growth temperature of 480 °C. After annealing, an improved optical property represented by a higher PL intensity compared to the conventional growth method (annealed, Tgrowth = 480 °C) was also obtained in the 1 µm-thick Ga0.94In0.06N0.01As0.99 thin film grown at low temperature of 380 °C.
INTRODUCTION Recently, GaInNAs alloys have found wide applications ranging from long-wavelength optical communication semiconductor lasers [1] to high-efficiency multi-junction solar cells [2]. The major advantage of this alloy is that the addition of a few atomic percent of N in GaAs causes a gigantic reduction in band gap energy, and that it can be favorably lattice matched to GaAs substrate by controlling the [N]/[In] composition ratio to ~ 3 [3, 4]. However, both the optical and electrical properties of GaInNAs films, in general, become increasingly degraded with increasing N composition [5-7]. The mechanism for the degradation is not fully understood at present, although a low miscibility of N in GaAs is known to strongly affect the growth mode, and segregation and clustering result during growth [7-8]. Recently, we have shown that irradiation of low-flux atomic hydrogen during RF-molecular beam epitaxy (H-MBE) results in an improved overall material quality since hydrogen acts as a suitable surfactant promoting a layer-by-layer growth mode [3-5]. As a continuing effort, we have investigated the effect of growth temperature on the crystal quality of Ga(In)NAs thin films grown by atomic H-assisted RF-MBE over a range of 340 ~ 520 °C. The crystal quality and optical properties were studied by high resolution X-ray diffraction (HR-XRD) and photoluminescence (PL) measurements.
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EXPERIMENTAL DETAILS The GaNxAs(1-x) and Ga0.94In0.06NxAs(1-x) thin films were grown on GaAs (100) substrates by atomic H-assisted RF-MBE [3-5]. Atomic H was irradiated to the substrate during both surface cleaning at 580 °C for 30 min, growth of 0.3 µm-thick GaAs buffer layer at 580 °C, and the following Ga(In)NAs epilayer. The growth rate was set to 0.8 ~1.0 µm/h, and growth temperature was varied over a range of 340 ~ 520 °C. The RF power and N2 flow rate were 190 ~ 200 W and 1 sccm, respectively. The N composition in Ga(In)NAs layers was determined by using high-resolution X-ray diffraction (HR-XRD), in which the relative shifts of
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