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MOCVD-grown heterostructures with one or several In[sub x]Ga[sub 1-x]N layers in a GaN matrix have been studied by transmission electron microscopy. In heterostructures with thick InGaN layers, a noncoherent system of domains with lateral dimensions (∼50 nm) on the order of the layer thickness (∼40 nm) is formed. In the case of ultrathin InGaN inclusions, nanodomains coherent with the GaN matrix are formed. The content of indium in nanodomains, determined by the DALI method, is as high as x ≈ 0.6 or more, substantially exceeding the average In concentration. The density of the nanodomains formed in the structures studied is n ≈ (2-5) x 10[sup 11] cm[sup -2]. In the structures with ultrathin InGaN inclusions, two characteristic nanodomain sizes are observed (3-6 and 8-15 nm). [ABSTRACT FROM AUTHOR]

Electrical properties and deep electron and hole traps spectra are compared for undoped n-GaN films grown by hydride vapor phase epitaxy (HVPE) in the regular process (standard HVPE samples) and in HVPE process optimized for decreasing the concentration of residual donor impurities (improved HVPE samples). It is shown that the residual donor density can be reduced by optimization from ~ 1017 cm-3 to (2-5) x 1014 cm-3. The density of deep hole traps and deep electron traps decreases with decreased donor density, so that the concentration of deep hole traps in the improved samples is reduced to ~5 x 1013 cm-3 versus 2.9 x 1016 cm-3 in the standard samples, with a similar decrease in the electron traps concentration. [ABSTRACT FROM AUTHOR]

The results of the investigation of low-temperature time-resolved photoluminescence in undoped and Si-doped In[sub 0.2]Ga[sub 0.8]N/GaN structures, which contain 12 quantum wells of width 60 Å separated by barriers of width 60 Å, are reported. The structures were grown by the MOCVD technique on sapphire substrates. The photoluminescence properties observed are explained by the manifestation of two-dimensional donor-acceptor recombination. These properties are the high-energy shift of the peak upon increasing the pumping intensity, a low-energy shift with increasing delay time, and a power law of luminescence decay of the t[sup -γ] type. The estimates of the total binding energy for donor and acceptor centers are given. This energy is 340 and 250 meV for Si-doped and undoped quantum wells, respectively. The role of the mosaic structure, which is typical for Group III hexagonal nitrides, is discussed as a factor favorable for the formation of donoracceptor pairs. [ABSTRACT FROM AUTHOR]

The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4-5 nm at a growth temperature of 720 °C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects. [ABSTRACT FROM AUTHOR]