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The normal-incidence reflectance measurement was employed to obtain the free exciton transition energy (E[sub FX]) of AlGaN alloys in Al[sub x]Ga[sub 1-x]N/GaN/sapphire heterostructure grown by metalorganic chemical vapor deposition. It was found that the thickness variation of the AlGaN layer may cause a noticeable change in the line shape of reflectance spectrum and impede the identification of the desired excitonic position. By using a reflection model of two absorbing layers with a transparent substrate, the experimental reflectance spectra were theoretically simulated and utilized to explain the reflection mechanism in Al[sub x]Ga[sub 1-x]N/GaN heterostructures. On the basis of the above analysis, the feasibility of the reflectance measurement for such heterostructures is confirmed. At room temperature, the E[sub FX]s obtained from the fitting showed an excellent agreement with the corresponding peak energies in the photoluminescence spectra. Furthermore, at the optical energy position about 100 meV above the E[sub FX], the spectral feature of exciton-LO phonon interaction was observed in the reflectance spectrum record for low Al composition (x≤0.16). Using the Al mole fraction derived from x-ray diffraction measurement, the bowing parameter of the epitaxial AlGaN layer was determined. In the range of 0≤x<0.3, the resulting bowing parameter shows a downward value of 0.53 eV. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the characteristics and degradation of an InGaN/AlGaN double-heterostructure light-emitting diode. Metalorganic chemical vapor deposition on a sapphire substrate; Electrical and optical degradations under high injected current density and high ambient temperature; Observations of electroluminescence, electron-beam induced current and cathodoluminescence.

Low-temperature AlN grown on AlGaN/GaN heterostructure in situ by metal-organic chemical vapor deposition is used as gate insulator and passivation layer to form quasi-normally-off field-effect transistors on 4 in. silicon substrate. The AlN layer not only increases the sheet carrier density and mobility, which results in the increase of the maximum drain current and transconductance, but also decreases gate leakage and current collapse. Simulated band diagrams indicate that only a small potential difference exists between the AlN surface barrier height and the AlN/AlGaN interface. We show that low-temperature grown AlN is effective in suppressing trapping effects and in improving device performance. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN heterostructures (HSs) with high two dimensional electron gas mobility (1070 cm2/V s) were grown on nonpolar a-plane (1120) sapphire substrate by metal organic chemical vapor deposition. High crystalline quality (reduced screw, edge, and mixed dislocations) with small root mean square surface roughness and small peak-valley distance values were observed in a-plane sapphire grown AlGaN/GaN HSs. Hexagonal-GaN phase was also observed on a-plane sapphire grown AlGaN/GaN HSs. An average increase of ns up to 22% for a plane and 26% for c plane were found after Si3N4 passivation. The product of ns and μH also increases for both a-plane (19%) and c-plane (28%) sapphire grown AlGaN/GaN HSs in a wide range of measurement temperature (87–400 K). The enhancement of sheet carrier density by Si3N4 passivation for nonpolar (1120) sapphire grown AlGaN/GaN HSs is a useful result for the design of future GaN high-electron-mobility transistors. [ABSTRACT FROM AUTHOR]

A non-recessed-gate enhancement-mode HEMT was fabricated on an undoped quaternary AlInGaN/GaN heterostructure with a thin barrier AlInGaN layer. The maximum drain current of 252 mA/mm and peak transconductance of 175 mS/mm were obtained on a 2 µm-length-gate HEMT with a large threshold voltage of 0.57 V. The enhancement-mode operation was observed in a large source-drain voltage range up to 40 V. The results imply that AlInGaN is a promising candidate for high power and high frequency applications. [ABSTRACT FROM AUTHOR]

Undoped AlInGaN/GaN heterostructure field-effect transistors (HFETs) have been demonstrated on sapphire substrate. The maximum drain current of 758 mA/mm and extrinsic transconductance of 123 mS/mm were obtained from the device with 2 μm gate length and 15 μm gate width. Such performance was comparable to that of a conventional modulation-doped (MOD) AlGaN/GaN HFET fabricated at same the condition. In spite of the high-density two-dimentional electron gas formed at the heterointerface, the AlInGaN/GaN HFET structure showed relatively low Hall mobility (689 cm2/V s at 300 K), which was due to the high concentration background doping in the undoped AlInGaN barrier region. Encouragingly, both the gate leakage current and drain current collapse showed lower values than that of the MOD-AlGaN/GaN HFET, which implied the potential application of quaternary AlInGaN to high-power and high-frequency devices. [ABSTRACT FROM AUTHOR]

Al0.26Ga0.74N/AlN/GaN heterostructures with 1-nm-thick AlN interfacial layers were grown on 100-mm-diam epitaxial AlN/sapphire templates and sapphire substrates by metalorganic vapor phase epitaxy. It was found that AlN/sapphire templates significantly enhanced the electron mobility of the two-dimensional electron gas (2DEG) confined at the GaN channel. This can be explained by the high-crystal-quality GaN channel realized by the use of epitaxial AlN/sapphire templates as substrates. The very high Hall mobilities of approximately 2100 cm2/V s at room temperature and approximately 17 000 cm2/V s at 77 K with a 2DEG density of approximately 1×1013/cm2 were uniformly obtained for AlGaN/AlN/GaN heterostructures on 100-mm-diam epitaxial AlN/sapphire templates. The Hall mobility of AlGaN/AlN/GaN heterostructures on epitaxial AlN/sapphire templates reached a very high value of 25 500 cm2/V s at 15 K. [ABSTRACT FROM AUTHOR]

The high-electron-mobility transistors (HEMTs) have been demonstrated on both sapphire and semi-insulating (SI) SiC substrates, and the dc characteristics of the fabricated devices were examined at temperatures ranging from 25 to 500 °C. The decrease in drain current and the transconductance with the increase of temperature have been observed. The decrease ratio of transconductance and drain current was similar for both the HEMTs on sapphire and SI-SiC substrates at and above 300 °C. The HEMTs on SiC substrates showed better dc characteristics after being subjected to thermal stress up to 500 °C. Although the SiC-based HEMTs showed better characteristics up to the temperature of 300 °C, compared with the sapphire-based HEMTs, similar dc characteristics were observed on both at and above 300 °C. For high-temperature applications (≥300 °C), additional cooling arrangements are essential for both devices. [ABSTRACT FROM AUTHOR]

We demonstrate the first room-temperature low-threshold continuous-wave (cw) operation of Al0.3Ga0.7As/GaAs single quantum well (SQW) heterostructure lasers grown by metalorganic chemical vapor deposition (MOCVD) on Si substrates using techniques of SiO2 back coating and thermal cycle annealing. The all-MOCVD-grown SQW lasers on GaAs/Si with etch pit density of 1.5× 107 cm-2 have threshold current as low as 55 mA (1.41 kA/cm2) under cw at room temperature. The SiO2 back coating is effective to obtain excellent current-voltage characteristics. Thermal cycle annealing is also found to improve the crystallinity of GaAs/Si and to contribute to room-temperature cw operation of the lasers on Si substrates. [ABSTRACT FROM AUTHOR]

High-voltage AlGaN/GaN heterostructure field-effect transistors (HFETs) with graded gate field-plate (FP) structures were fabricated to investigate the effectiveness of a linearly graded FP structure on current collapse. To improve the reproducibility of the FP structure manufacturing process, a simple process for a linearly graded SiO2 profile formation was developed. A HFET with a 23°-angle FP exhibited a significantly decreased on-resistance increase ratio of 1.16 after application of a drain bias of 600 V. [ABSTRACT FROM AUTHOR]