Single Phase InGaN Research Articles

Phase separation suppression in InxGa1−xN on a Si substrate using an indium modulation technique

A high quality, single phase InGaN film is fabricated on a GaN/Si (111) substrate by optimizing the pulse patterned In supply with a plasma-assisted MBE technique. Compositional phase separation in InGaN is considerably suppressed. The optical and structural properties of the single phase InGaN epitaxial film are consistently confirmed by atomic force microscopy, X-ray diffraction and photoluminescence measurements. We propose a growth mechanism for single phase InGaN in terms of optimal incorporation and surface migration of In atoms.

Growth and electrical transport properties of InGaN/GaN heterostructures grown by PAMBE

InGaN epitaxial films were grown on GaN template by plasma-assisted molecular beam epitaxy. The composition of indium incorporation in single phase InGaN film was found to be 23%. The band gap energy of single phase InGaN was found to be ∼2.48eV. The current–voltage (I–V) characteristic of InGaN/GaN heterojunction was found to be rectifying behavior which shows the presence of Schottky barrier at the interface. Log–log plot of the I–V characteristics under forward bias indicates the current conduction mechanism is dominated by space charge limited current mechanism at higher applied voltage, which is usually caused due to the presence of trapping centers. The room temperature barrier height and the ideality factor of the Schottky junction were found to 0.76eV and 4.9 respectively. The non-ideality of the Schottky junction may be due to the presence of high pit density and dislocation density in InGaN film.

Growth and Characterization of a-plane In0.2Ga0.8N/ GaN hetrostructures on r-Sapphire

ABSTRACTNon-polar a-plane InGaN films were grown on a r-plane sapphire substrate by plasma assisted molecular beam epitaxy (PAMBE). The growth temperature and Indium flux were varied to optimize the desired composition of In0.23Ga0.77N on the (11-20) a-plane GaN epilayer grown on a (1-102) r-plane sapphire substrate. The structural, morphological and optical properties of the optimized composition have been studied. It was found that highly a-axis oriented InGaN epilayers with no phase separation can be grown at 540 °C with In/Ga flux ratio of 0.72. The composition of indium incorporation in single phase InGaN films was found to be 23% as estimated by high resolution X-ray diffraction. The room temperature band gap energy of single phase InGaN layers was determined by photoluminescence measurement and found to be around 2.56 eV.

P-type InGaN across the entire alloy composition range

A systematic investigation on Mg doped and undoped InGaN epilayers grown by plasma-assisted molecular beam epitaxy has been conducted. Single phase InGaN alloys across the entire composition range were synthesized and Mg was doped into InxGa1−xN (0.1 ≤ x ≤ 0.88) epilayers up to ∼1020/cm3. Hall effect, thermopower, and electrochemical capacitance voltage experimental results demonstrate the realization of p-type InGaN across the entire alloy composition range for properly Mg doped InGaN. Hole densities have been measured or estimated to be in the lower ∼1018/cm3 range when the net acceptor concentrations are in the lower ∼1019/cm3 range across the composition range.

Semibulk InGaN: A novel approach for thick, single phase, epitaxial InGaN layers grown by MOVPE

In this paper we demonstrate a solution to systematically obtain thick, single phase InGaN epilayers by MOVPE. The solution consists in periodically inserting ultra-thin GaN interlayers during InGaN growth. Measurements by HAADF-STEM, X-ray diffraction, cathodoluminescence and photoluminescence demonstrate the effective suppression of the three-dimensional sublayer that is shown to spontaneously form in control InGaN epilayers grown without this method. Simulation predicts that tunneling through the GaN barriers is efficient and that carrier transport through this semi-bulk InGaN/GaN structure is similar to that of bulk InGaN. Such structures may be useful for improving the efficiency of InGaN solar cells by allowing thicker, higher quality InGaN absorption layers.

Si/InGaN Core/Shell Hierarchical Nanowire Arrays and their Photoelectrochemical Properties

Three-dimensional hierarchical nanostructures were synthesized by the halide chemical vapor deposition of InGaN nanowires on Si wire arrays. Single phase InGaN nanowires grew vertically on the sidewalls of Si wires and acted as a high surface area photoanode for solar water splitting. Electrochemical measurements showed that the photocurrent density with hierarchical Si/InGaN nanowire arrays increased by 5 times compared to the photocurrent density with InGaN nanowire arrays grown on planar Si (1.23 V vs RHE). High-resolution transmission electron microscopy showed that InGaN nanowires are stable after 15 h of illumination. These measurements show that Si/InGaN hierarchical nanostructures are a viable high surface area electrode geometry for solar water splitting.

Evolution of phase separation in In-rich InGaN alloys

Evolution of phase separation in InxGa1−xN alloys (x∼0.65) grown on AlN/sapphire templates by metal organic chemical vapor deposition has been probed. It was found that growth rate, GR, is a key parameter and must be high enough (>0.5 μm/h) in order to grow homogeneous and single phase InGaN alloys. Our results implied that conditions far from thermodynamic equilibrium are needed to suppress phase separation. Both structural and electrical properties were found to improve significantly with increasing GR. The improvement in material quality is attributed to the suppression of phase separation with higher GR. The maximum thickness of the single phase epilayer tmax (i.e., maximum thickness that can be grown without phase separation) was determined via in situ interference pattern monitoring and found to be a function of GR. As GR increases, tmax also increases. The maximum value of tmax for In0.65Ga0.35N alloy was found to be ∼1.1 μm at GR>1.8 μm/h.

Growth temperature - phase stability relation in In1-xGaxN epilayers grown by high-pressure CVD

AbstractThe influence of the growth temperature on the phase stability and composition of single-phase In1-xGaxN epilayers has been studied. The In1-xGaxN epilayers were grown by high-pressure Chemical Vapor Deposition with nominally composition of x = 0.6 at a reactor pressure of 15 bar at various growth temperatures. The layers were analyzed by x-ray diffraction, optical transmission spectroscopy, atomic force microscopy, and Raman spectroscopy. The results showed that a growth temperature of 925°C led to the best single phase InGaN layers with the smoothest surface and smallest grain areas

Single phase InxGa1−xN (0.25≤x≤0.63) alloys synthesized by metal organic chemical vapor deposition

We present the results of single phase InxGa1−xN alloys for the In composition ranging from 25% to 63% synthesized by metal organic chemical vapor deposition. Single peak of x-ray diffraction θ-2θ scans of the (002) plane in InGaN alloys confirms that there is no phase separation. It was found both electron mobility and concentration increase with an increase of In content. Atomic force microscopy measurements revealed that the grown films have a surface roughness that varies between 1.5 and 4.0 nm and are free from In droplets. The results suggest that it is possible to synthesize single phase InGaN alloys inside the theoretically predicted miscibility gap.

Phase separation in InGaN grown by metalorganic chemical vapor deposition

We report on phase separation in thick InGaN films with up to 50% InN grown by metalorganic chemical vapor deposition from 690 to 780 °C. InGaN films with thicknesses of 0.5 μm were analyzed by θ–2θ x-ray diffraction, transmission electron microscopy (TEM), and selected area diffraction (SAD). Single phase InGaN was obtained for the as-grown films with <28% InN. However, for films with higher than 28% InN, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN.