Growth and properties of InN, InGaN, and InN/InGaN quantum wells

Abstract

This paper describes our recent progress on InN, In‐rich Inx Ga1–x N, and InN/Inx Ga1–x N quantum wells (QWs) grown by radio‐frequency plasma‐assisted molecular‐beam epitaxy. Among the essential growth sequences to obtain high‐quality InN, the nitridation process of (0001) sapphire substrates was reexamined. It was found that the lower‐temperature and longer–period nitridation‐process was very effective in improving crystalline quality of InN films. We succeeded in dramatically improving c ‐axis orientation of InN films without deteriorating their a ‐axis orientation by nitridating the substrates at a relatively low‐temperature of 300 °C for a relatively long period of 2 h. The full widths at half maximum (FWHMs) of (0002) X‐ray rocking curves as narrow as 1 arcmin were obtained from only 400 nm thick InN films. These FWHMs are the narrowest value ever reported for InN and moreover approximately a twentieth part of the values obtained from our conventional InN films with a similar thickness, which were grown via the conventional nitridation process carried out at 550 °C for 1 h. Furthermore interference fringes in X‐ray diffraction (ω –2θ scan) were observed from these improved InN films. These high crystalline quality InN layers have been employed as a template for the growth of In‐rich Inx Ga1–x N layers (0.70 ≤ x ≤ 0.94). The resultant Inx Ga1–x N layers have shown dramatic improvements in not only the surface morphology but also both the a ‐ and c ‐axis orientations. By employing In0.8Ga0.2N layers of improved quality as the bottom barrier layer, InN/In0.8Ga0.2N multiple quantum well (MQW) and single quantum well (SQW) structures with different well widths were fabricated. Clear satellite peaks of X‐ray diffraction were observed from these MQW structures. Both of these SQW and MQW structures have exhibited a blue shift of the photoluminescence peak energy with decreasing well width. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of In-Rich In x Al1−x N Films on (0001) Sapphire by RF-MBE and their Properties

“…The modified-nitridation samples exhibited smaller XRC FWHM values than those of the conventional-nitridation samples, verifying that the tilt distribution in the In x Al 1-x N films were indeed improved by employing the modified nitridation process, as expected from our previous experience with InN 21 and In-rich In x Ga 1-x N. 22 The XRC FWHM increased with decreasing x for the conventional-nitridation samples. This tendency is very similar to that for In-rich In x Ga 1-x N. 22,23 On the other hand, the modifiednitridation samples showed a similar tendency for x from 1 down to 0.76; however, the FWHM decreased with the further decrease in x. Although further studies are necessary, we assume that this sudden decrease in FWHM is associated with the formation of sharp nano-columns as shown in Fig.…”

“…As for the twist distribution in the films, we tried to determine the FWHM value of the (10 " 10) XRC from the FWHM values of the (0002), (10 " 13), (10 " 12), (10 " 11), and (30 " 32) XRCs for each sample in the same manner as our previous studies on In-rich In x Ga 1-x N. 22 The XRC intensities for asymmetrical reflections, however, suddenly became weak and noisy with decreasing x. We could determine the (10 " 10) XRC FWHM for only a few samples including InN and could not obtain informative data sets.…”

“…We report not only the optical absorption (OA) but also photoluminescence (PL) properties of these In-rich In x Al 1-x N films. We also show that substrate nitridation with lower temperature and longer period conditions is effective for producing a narrower tilt distribution in the In-rich In x Al 1-x N films as is the case for InN 21 and In-rich In x Ga 1-x N. 22 …”

High-Resolution Electron Microscopy of Semiconductor Heterostructures and Nanostructures

“…After this, important improvements were achieved regarding smaller sizes and higher densities [101][102][103][104][105][106][107], and recently the emission, even very poor, of InN QDs [108,109] and growth and optical properties of cubic InN dots [110] have been reported. Other types of InN nanostructures fabricated so far include single [111] and multiple [112][113][114][115] quantum wells, nanocolumns [116,117], and nanowires [118][119][120]. However, even if the number of publications related to these nanomaterials has increased considerably during the last years, the number of them including characterization by HRTEM still remains scarce.…”

Polarity dependence of In‐rich InGaN ternary alloys grown by RF‐MBE

“…In these reports, polarity and growth temperature dependences on crystalline quality of InN were investigated in detail and precise control of growth condition was very important to improve its crystalline quality. However, as for RF-MBE growth of In-rich InGaN alloys, there are a few reports of their crystalline quality depending on precise epitaxy-control until now [7,8]. …”