Phase separation in InGaN thick films and formation of InGaN/GaN double heterostructures in the entire alloy composition

Abstract

We report the growth of InGaN thick films and InGaN/GaN double heterostructures by molecular beam epitaxy at the substrate temperatures 700–800 °C, which is optimal for the growth of GaN. X-ray diffraction and optical absorption studies show phase separation of InN for InxGal−xN thick films with x>0.3. On the other hand, InxGal−xN/GaN double heterostructures show no evidence of phase separation within the detection capabilities of our methods. These observations were accounted for using Stringfellow’s model on phase separation, which gives a critical temperature for miscibility of the GaN–InN system equal to 2457 K.

Limits and accuracy of valence force field models forInxGa1−xNalloys

“…The F M (1) and F M (2) are the corrections given by Martin with respect to the original Keating model. F X (1) and F X (2) represent the additional corrections if the change of the d parameter is considered. From Eqs.…”

“…An important issue for In x Ga 1Ϫx N alloys is homogeneity: Experimentally it has been found that these alloys are often unstable against phase separation, spatial fluctuations in the In concentration, or partial ordering. [1][2][3][4] These effects have been shown to strongly affect the luminescence efficiency. It is therefore crucial to get a deeper insight into the energetics and local atomic structure of In x Ga 1Ϫx N alloys.…”

Response to “Comment on ‘Direct evidence of nanocluster-induced luminescence in InGaN epifilms’ ” [Appl. Phys. Lett. 87, 136101 (2005)]

“…8 Our XRD measurements clearly indicate strong indium aggregation processes in our sample and this observation is in agreement with previous reports. [4][5][6][7][8] The comments also argued the interpretation of our scanning electron microscopy ͑SEM͒ and energy dispersive x-ray spectrometry ͑EDS͒ results. Our InGaN films have been found to have mirrorlike surface by scanning electron microscopy ͑SEM͒ and transmission electron microscopy ͑TEM͒ measurements.…”

“…This result has been widely discussed in the nitride materials. [4][5][6][7] The correspondence of the appearance of multiple x-ray diffraction peaks in InGaN thin film to the phase separation over the surface has been clearly established. It has also been shown to correlate with double luminescence peaks.…”

“…Besides, there are many other excellent works that reported the observation of nanoscale indium composition fluctuations due to phase separation by different techniques. [6][7][8][9][10][11][12][13] For example, it was found that in the growth of InGaN films, the composition pulling effect is inevitable and plays an important role in the microstructure. It initially inhibits the incorporation of In during the earlier stages.…”