A-plane InN Research Articles

Microstructure of A ‐plane InN grown on R ‐plane sapphire by ECR‐MBE

We used electron cyclotron resonance plasma-excited molecular beam epitaxy (ECR-MBE) to grow A-plane (110) InN on nitridated R-plane (102) sapphire and then measured the structural properties using transmission electron microscopy (TEM). We determined the epitaxial relationship between A-plane InN and R-plane sapphire to be (110)InN // (102)sapphire and [100]InN // [110]sapphire. Moreover, the results indicated that the nitridation of the sapphire produced a (001) cubic AlN layer, and this layer caused the subsequent InN to have its a-axis normal to the interface. Also, by using two diffraction vector orientations in the TEM measurement, we found that dislocations with a screw component had a density of about 5 × 1010 cm–2, which is about ten times higher than that with an edge component. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of A ‐plane (11‐20) In‐rich InGaN on R ‐plane (10‐12) sapphire by RF‐MBE

Non-polar A-plane (11-20) high In content (In-rich) InGaN was grown on R-plane (10-12) sapphire with an InN template by radio-frequency plasma assisted molecular beam epitaxy (RF-MBE). Nitridation of R-plane sapphire was carried out at 300 °C for 2 hours by RF-nitrogen plasma. A template of A-plane InN was grown at 400 °C. The In-rich InGaN films were then grown at the same temperature on the InN template. We characterized the films using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photo-luminescence (PL). These results indicated clearly that non-polar In0.71Ga0.29N was successfully obtained with a PL emission at approximately 1.1 eV. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

RF-MBE growth of a-plane InN on r-plane sapphire with a GaN underlayer

a-Plane InN films were grown on r-plane sapphire substrates with GaN underlayers by RF-N 2 plasma molecular beam epitaxy (MBE). X-ray diffraction (XRD) measurements and reflection high-energy electron diffraction (RHEED) observation revealed that the InN films were grown with InN (1 1 2¯ 0)∥GaN (1 1 2¯ 0)∥sapphire (2 2¯ 0 4). We have carried out micro-Raman scattering measurements for a-plane InN film. Raman peaks were observed at 448, 490 and 598 cm −1, which can be identified as the A 1 transversal optical (TO), E 2 (high) and E 1 longitudinal optical (LO) mode phonon, respectively. We also carried out photoluminescence (PL) measurements for a-plane InN film. Strong PL was observed between 0.62 and 0.65 eV, which is the lowest ever reported for InN. It is suggested from the excitation intensity and temperature dependence of the PL spectra that the red shift of the PL peak is due to the Franz–Keldysh effect.

Polarized photoluminescence and absorption in A-plane InN films

The authors report the observation of strong polarization anisotropy in the photoluminescence (PL) and the absorption spectra of [112¯0] oriented A-plane wurtzite InN films grown on R-plane (11¯02) sapphire substrates using molecular beam epitaxy. For A-plane films the c axis lies in the film plane. The PL signal collected along [112¯0] with electric vector E⊥c is more than three times larger than for E‖c. Both PL signals peak around 0.67eV at 10K. The absorption edge for E‖c is shifted to higher energy by 20meV relative to E⊥c. Optical polarization anisotropy in wurtzite nitrides originates from their valence band structure which can be significantly modified by strain in the film. The authors explain the observed polarization anisotropy by comparison with electronic band structure calculations that take into account anisotropic in-plane strain in the films. The results suggest that wurtzite InN has a narrow band gap close to 0.7eV at 10K.

A-plane (110) InN growth on nitridatedR-plane (102) sapphire by ECR-MBE

A-plane (110) InN has been successfully grown on R-plane (102) sapphire substrate by electron cyclotron resonance (ECR) plasma-exited molecular beam epitaxy through substrate nitridation process. The substrate nitridation of R-plane sapphire by ECR nitrogen plasma was carried out at 430 °C for 10 and 15 min. The results of reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and scanning electron microscopy indicated the formation of A-plane InN on R-plane sapphire. Inclusion of cubic InN was also observed together with A-plane InN through RHEED and XRD measurements in case of A-plane InN layer grown on 10 min nitridated substrate. However, when the nitridation time of R-plane sapphire by ECR nitrogen plasma increased to 15 min, it is confirmed that formation of cubic InN was successfully suppressed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of a-plane InN on r-plane sapphire with a GaN buffer by molecular-beam epitaxy

We report heteroepitaxial growth of InN on r-plane sapphire substrates with an AlN nucleation layer and GaN buffer using plasma-assisted molecular-beam epitaxy. The InN film was identified to be nonpolar (112̄0) a-plane which follows the a-plane GaN buffer. Optical absorption and photoluminescence measurements of this material show that InN has a fundamental band gap of about 0.7 eV, which is also seen for growth on c-plane sapphire. The room-temperature Hall mobility of undoped a-plane InN is around 250 cm2/V s with a carrier concentration around 6×1018 cm−3. We also studied the electrical properties of the a-plane InN as a function of film thickness. In contrast to c-plane InN grown on c-plane sapphire, we did not observe apparent improvement of electrical properties of a-plane InN by growing thicker films.

Growth of non-polar a-plane and cubic InN on r-plane sapphire by molecular beam epitaxy

ABSTRACTGrowth of non-polar III-nitrides has been an important subject recently due to its potential improvement on the efficiency of III-nitride-based opto-electronic devices. Despite study of non-polar GaN and GaN-based heterostructures, there are few reports on epitaxial growth of non-polar InN, which is also an important component of the III-nitride system. In this study, we report heteroepitaxial growth of non-polar InN on r-plane sapphire substrates using plasma-assisted molecular beam epitaxy. It is found that when a GaN buffer is used, the following InN film appears to be non-polar (1120) a-plane which follows the a-plane GaN buffer. The room temperature Hall mobility of undoped a-plane InN is around 250 cm2/Vs with a carrier concentration around 6×1018 cm-3. Meanwhile, if InN film is directly deposited on r-plane sapphire without any buffer, the InN layer is found to consist of a predominant zincblende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase with increasing content with proceeding growth.