Nitrogen incorporation rate, optimal growth temperature, and AsH3-flow rate in GaInNAs growth by gas-source MBE using N-radicals as an N-source

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Abstract

We have investigated the conditions for growing GaInNAs by gas-source MBE using N-radicals as an N-source. The optimal growth temperature of GaInNAs with good surface morphology and PL characteristics was clarified: at higher growth temperature, the surface morphology degraded. On the other hand, PL intensity became weak at temperatures lower than the optimal one. This trend is similar to that in GaInAs grown by MBE. AsH3-flow rate mainly affected crystal quality of GaInNAs rather than incorporation of nitrogen atoms. It was also confirmed experimentally that the N-radicals produced by RF-discharge are incorporated in the epitaxial layer like dopant atoms, indicating that their sticking coefficient is about one. This result is unlike that for the MOCVD growth using dimethylhydrazine as an N-source. These results are crucial to further improve the crystal quality of GaInNAs.

Introduction

GaInNAs is one of the mixed group-V nitride-alloy semiconductors whose band gap shrinks with decrease of lattice constant at small N-content region due to high electro-negativity of nitrogen atoms [1]. This behavior is quite different from that of conventional III–V alloy semiconductors. By taking advantage of its unique physical properties, GaInNAs should be able to confine electrons in the wells effectively and to emit in the 1.3- or 1.55-μm range on a GaAs substrate [2]. As a result, GaInNAs has been intensively investigated for its application in long-wavelength semiconductor lasers with excellent temperature performance for optical-fiber communications. The lasing operation of a GaInNAs laser diode (GaInNAs-LD) in the 1.3-μm range was demonstrated [3], [4] and the pulsed lasing operation of a GaInNAs vertical-cavity surface-emitting laser (GaInNAs-VCSEL) at 1.2 μm was also reported [5]. We succeeded in growing GaInNAs by gas-source MBE (GS-MBE) using N-radicals as an N-source [2]. The metal-organic chemical-vapor-deposition (MOCVD) growth of GaInNAs using dimethylhydrazine (DMHy) as an N-source has been reported recently [6], [7], [8]. In general, the crystal quality of GaInNAs degrades with increase in N-content possibly due to phase-separation, even though the amount of strain in the layer decreases [6]. The optimization of the growth conditions as well as the growth methods is thus crucial in order to achieve good crystal quality of GaInNAs to further improve GaInNAs LDs.

In this report, we fully investigated various growth conditions, such as growth temperature, growth rate and AsH3-flow-rate, for the crystal growth of GaInNAs by GS-MBE. N-radicals were used as an N-source and we grew GaInNAs with better crystal quality. We also clarified the high sticking coefficient of nitrogen atoms (supplied by N-radicals) in the epitaxial layer.

Section snippets

Experiment

The GaInNAs layers were grown on a (1 0 0) GaAs substrate by gas-source molecular beam epitaxy (GS-MBE) in which the N-radical produced by RF discharge was used as an N-source. Growth temperature was 390–520°C, measured by a thermocouple gauge, growth rate was 0.2–1.0 μm/h, AsH3-flow-rate was 5–15 sccm, N2-flow rate was 0.04–1.00 sccm, and RF power was 300–400 W. The free-carrier concentration of the unintentionally doped Ga0.95In0.05N0.02As0.98 bulk layer, lattice matched to GaAs, was 3×1015 cm−3 of

Growth temperature

The Ga0.68In0.32N0.005As0.995 single layers with thickness of 6 nm were grown under different growth temperatures at 390, 460, and 520°C. The GaInAs layer with the same In content as GaInNAs was also grown at 460°C for reference. Fig. 1 shows the atomic-force-microscope (AFM) image of the samples. A smooth surface comparable to that of Ga0.68In0.32As was observed when the growth temperature was lower than 460°C. The root-mean-square (RMS) of surface roughness was estimated to be lower than 0.63 

Conclusions

We have clarified the optimal growth conditions for the crystal growth of GaInNAs by gas-source MBE with N-radicals as an N-source. The optimal values of the growth temperature and AsH3-flow rate for better crystal quality of GaInNAs were found to be 460°C and 10 sccm for a 1.3-μm GaInNAs SQW. From the analysis of growth rate dependence of N-content, we confirm that the sticking coefficient of nitrogen atoms supplied by N-radicals is about one. This result is quite different from that in the

Acknowledgements

We would like to thank Dr. M. Kuwahara for the atomic-force-microscope measurements.

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