We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Band parameters for nitrogen-containing semiconductors

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

AlGaN/GaN HEMTs-an overview of device operation and applications

The rapid development of the RF power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance GaN-based RF power devices have made substantial progresses in the last decade This paper attempts to review the latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, to achieve the state-of-the-art microwave and millimeter-wave performance The reliability and manufacturing challenges are also discussed

GaN-Based RF Power Devices and Amplifiers

GaN based HFETs are of tremendous interest in applications requiring high power at microwave frequencies. Although excellent current-voltage (I-V) characteristics and record high output power densities at microwave frequencies have been achieved, the origin of the 2DEG and the factors limiting the output power and reliability of the devices under high power operation remain uncertain. Drain current collapse has been the major obstacle in the development of reliable high power devices. We show that the cause of current collapse is a charging up of a second virtual gate, physically located in the gate drain access region. Due to the large bias voltages present on the device during a microwave power measurement, surface states in the vicinity of the gate trap electrons, thus acting as a negatively charged virtual gate. The maximum current available from a device during a microwave power measurement is limited by the discharging of this virtual gate. Passivated devices located adjacent to unpassivated devices on the same wafer show almost no current collapse, thus demonstrating that proper surface passivation prevents the formation of the virtual gate. The possible mechanisms by which a surface passivant reduces current collapse and the factors affecting reliability and stability of such a passivant are discussed.

The impact of surface states on the DC and RF characteristics of AlGaN/GaN HFETs

GaN high-electron-mobility-transistors (HEMTs) on SiC were fabricated with field plates of various dimensions for optimum performance Great enhancement in radio frequency (RF) current-voltage swings was achieved with acceptable compromise in gain, through both reduction in the trapping effect and increase in breakdown voltages When biased at 120 V, a continuous wave output power density of 322 W/mm and power-added efficiency (PAE) of 548% at 4 GHz were obtained using devices with dimensions of 055/spl times/246 /spl mu/m/sup 2/ and a field-plate length of 11 /spl mu/m Devices with a shorter field plate of 09 /spl mu/m also generated 306 W/mm with 496% PAE at 8 GHz Such ultrahigh power densities are a dramatic improvement over the 10-12 W/mm values attained by conventional gate GaN-based HEMTs

30-W/mm GaN HEMTs by field plate optimization

In this letter, a novel heterojunction AlGaN/AlN/GaN high-electron mobility transistor (HEMT) is discussed. Contrary to normal HEMTs, the insertion of the very thin AlN interfacial layer (/spl sim/1 nm) maintains high mobility at high sheet charge densities by increasing the effective /spl Delta/E/sub C/ and decreasing alloy scattering. Devices based on this structure exhibited good DC and RF performance. A high peak current 1 A/mm at V/sub GS/=2 V was obtained and an output power density of 8.4 W/mm with a power added efficiency of 28% at 8 GHz was achieved.

AlGaN/AlN/GaN high-power microwave HEMT

GaN high electron mobility transistors (HEMTs) were fabricated using an overlapping-gate technique in which the drain-side edge of the metal gate overlaps on a high breakdown and high dielectric constant dielectric. The overlapping structure reduces the electric field at the drain-side gate edge, thus increasing the breakdown of the device. A record-high three-terminal breakdown figure of 570 V was achieved on a HEMT with a gate-drain spacing of 13 /spl mu/m. The source-drain saturation current was 500 mA/mm and the extrinsic transconductance 150 mS/mm.

High breakdown GaN HEMT with overlapping gate structure

Two schemes of nucleation and growth of gallium nitride on Si(111) substrates are investigated and the structural and electrical properties of the resulting films are reported. Gallium nitride films grown using a 10–500 nm-thick AlN buffer layer deposited at high temperature (∼1050 °C) are found to be under 260–530 MPa of tensile stress and exhibit cracking, the origin of which is discussed. The threading dislocation density in these films increases with increasing AlN thickness, covering a range of 1.1 to >5.8×109 cm−2. Films grown using a thick, AlN-to-GaN graded buffer layer are found to be under compressive stress and are completely crack free. Heterojunction field effect transistors fabricated on such films result in well-defined saturation and pinch-off behavior with a saturated current of ∼525 mA/mm and a transconductance of ∼100 mS/mm in dc operation.

Metalorganic chemical vapor deposition of GaN on Si(111): Stress control and application to field-effect transistors

In this article, we discuss parameters influencing (a) the properties of thin AlxGa1−xN layers grown by metalorganic chemical vapor deposition and (b) the electrical properties of the two-dimensional electron gas (2DEG) forming at the AlxGa1−xN/GaN heterojunction. For xAl>0.3, the AlxGa1−xN layers showed a strong tendency towards defect formation and transition into an island growth mode. Atomically smooth, coherently strained AlxGa1−xN layers were obtained under conditions that ensured a high surface mobility of adsorbed metal species during growth. The electron mobility of the 2DEG formed at the AlxGa1−xN/GaN interface strongly decreased with increasing aluminum mole fraction in the AlxGa1−xN layer and increasing interface roughness, as evaluated by atomic force microscopy of the surfaces prior to AlxGa1−xN deposition. In the case of modulation doped structures (GaN/AlxGa1−xN/AlxGa1−xN:Si/AlxGa1−xN), the electron mobility decreased with decreasing thickness of the undoped spacer layer and increasing sil...

N.-Q. Zhang

Papers

The impact of surface states on the DC and RF characteristics of AlGaN/GaN HFETs

AlGaN/AlN/GaN high-power microwave HEMT

High breakdown GaN HEMT with overlapping gate structure

Metalorganic chemical vapor deposition of GaN on Si(111): Stress control and application to field-effect transistors

Metalorganic chemical vapor deposition of high mobility AlGaN/GaN heterostructures