GaN high electron mobility transistors (HEMTs) were monolithically integrated with silicon CMOS to create a functional current mirror circuit. The integrated circuit was fabricated on 100 mm diameter modified silicon-on-insulator (SOI) wafers incorporating a resistive (111) silicon handle substrate and a lightly doped (100) silicon device layer. In a CMOS-first process, the CMOS was fabricated using the (100) device layer. Subsequently GaN was grown by plasma molecular beam epitaxy in windows on the (111) handle substrate surface without wire growth despite using gallium-rich growth conditions. Transmission lines fabricated on the GaN buffer/SOI wafer exhibited a microwave loss of less than 0.2 dB/mm up to 35 GHz. Direct current measurements on GaN HEMTs yielded a current density of 1.0 A/mm and transconductance of 270 mS/mm. At 10 GHz and a drain bias of 28 V, 1.25 mm long transistors demonstrated a small signal gain of 10.7 dB and a maximum power added efficiency of 53% with a concomitant power of 5.6 W. The silicon and GaN transistors were interconnected to form high yield test interconnect daisy chains and a monolithic current mirror circuit. The CMOS output drain current controlled the GaN transistor quiescent current and consequently the microwave gain.

GaN high electron mobility transistor (HEMT) structures have been grown by plasma molecular beam epitaxy on 100 mm diameter ⟨111⟩ silicon substrates. Crack-free films with thicknesses of up to 1.7 μm were deposited without the use of strain-relaxing buffer layers. X-ray measurements indicate high structural uniformity and the Pendellosung oscillations are observed due to the abruptness of the AlGaN/GaN interface. Capacitance-voltage measurements display a sharp pinch-off with a depleted GaN buffer layer and no measurable charge accumulation at the substrate-epi interface. Transmission line measurements on the GaN HEMT buffer and substrate indicate a loss of less than 0.2 dB/mm up to 20 GHz. An average sheet resistance of 443 Ω/sq with a standard deviation of 0.8% and a mobility of 1600 cm2/V s were obtained for an Al0.25Ga0.75N/GaN HEMT. Transistors were fabricated with a current density of 1.2 A/mm and a transconductance of 290 mS/mm which is quite comparable to GaN HEMTs on SiC.

Effect of the growth temperature and the AlN mole fraction on In incorporation and properties of quaternary IIInitride layers grown by molecular beam epitaxy J. Appl. Phys.In incorporation during the growth of quaternary III-nitride compounds by plasma-assisted molecular beam epitaxy Appl. Phys. Lett. 82, 2242Lett. 82, (2003; 10.1063/1.1566465Incorporation-related structural issues for beryllium doping during growth of GaN by rf-plasma molecular-beam epitaxy Appl.The conventional approach to growth of the nitride films GaN, AlN, InN, and their alloys by rf plasma molecular beam epitaxy uses metal-rich surface conditions due to improved material quality compared to nitrogen-rich conditions. The surface metal may incorporate into the growing film, act as a surfactant, and/or react with the underlying film or substrate. Using a simple chemical exchange reaction model and tabulated thermodynamic data at molecular beam epitaxy growth temperatures the predicted preferential incorporation series on the column III site under metal-rich conditions is found to be AlϾ B , Be, Si, MgϾ GaϾ In, Fe. This series is consistent with the observed ternary growth behavior and surfactant order. The series is also consistent with silicon migration in AlN but not GaN, sharper beryllium transitions in GaN than AlN, the significant migration of iron in GaN, and the reactivity of AlN nucleation layers with SiC surfaces. The model is used to predict boron incorporation under metal-rich conditions in BGaN and BAlN and should prove useful as a tool in predicting the incorporation behavior of other cations during metal-rich epitaxial growth of nitride films and possibly other materials.

Articles you may be interested inStructural, morphological, and defect properties of metamorphic In0.7Ga0.3As/GaAs0.35Sb0.65 p-type tunnel field effect transistor structure grown by molecular beam epitaxy Material properties and performance of metamorphic optoelectronic integrated circuits grown by molecular beam epitaxy on GaAs substrates Metamorphic heterojunction bipolar transistor ͑M-HBT͒ structures and metamorphic P -I -N (M-PIN) photodiode structures were grown on GaAs substrates. A compositionally graded AlGaInAs buffer layer was used to expand the lattice constant to that of InP. Cross-sectional transmission electron micrographs of the M-HBT structure showed that the dislocations from compositional grading were predominantly localized in the buffer layer and that the device layers possessed planar interfaces. Secondary ion mass spectroscopy depth profiles of the 4ϫ10 19 cm Ϫ3 beryllium-doped In 0.53 Ga 0.47 As base layer exhibited sharp doping interfaces, indicating that metamorphic growth was not causing enhanced beryllium diffusion. The current gain of large emitter M-HBT devices approached the current gain for the same device structure grown on an InP substrate. A P -I -N photodiode structure was also grown metamorphically on a GaAs substrate and lattice matched on an InP substrate. Both types of photodiodes showed almost identical responsivities and bandwidths. A responsivity to 1.55 m radiation of 0.55 A/W, which corresponds to an external quantum efficiency of 44%, was obtained with M-PIN photodiodes. The 3 dB bandwidths exceeded 20 GHz for M-PIN photodiodes with diameters of 25 m or smaller. These results are very encouraging for the application of metamorphic technology to nonmajority carrier devices.

GaN high electron mobility transistor (HEMT) structures containing AlN nucleation layers were grown on SiC substrates by molecular beam epitaxy. Deleterious charge is observed near the GaN∕AlN interface when the AlN layer is grown using aluminum-rich growth conditions which promote AlN material quality. The unwanted charge is correlated with nondestructive mercury probe buffer leakage measurements and degraded capacitance-voltage profiles. Secondary ion mass spectrometry measurements on a HEMT structure with a thick AlN layer grown aluminum rich confirm that the unintentional dopant is silicon which rapidly migrates through the AlN layer to the GaN buffer layer. Leakage current measurements on aluminum-rich AlN layers indicate that the conduction is in the initial GaN layers near the GaN∕AlN interface. It is proposed that under aluminum-rich conditions the excess aluminum present on the growth surface in the liquid state is reacting with the substrate surface resulting in dissolved silicon that rapidly travels with the growth surface. Thermodynamic calculations and aluminum-silicon phase diagrams support this mechanism. By careful adjustment of the aluminum to nitrogen flux ratio, silicon outmigration is significantly reduced with a concomitant reduction in leakage current by four orders of magnitude.