InP Bi-CMOS technology capable of wafer-scale device-level heterogeneous integration (HI) of InP HBTs and CMOS has been developed. With this technology, full simultaneous utilization of III-V device speed and CMOS circuit complexity is possible. Simple ICs and test structures have been fabricated, showing no significant CMOS or HBT degradation and high heterogeneous interconnect yield. The heterogeneously integrated differential amplifiers with record performance and HBTs with fT=400 GHz were obtained. Thermal vias to the Si substrate provide sufficient heat path to lower HI HBT thermal resistances close to on-InP values. Resulting circuits maintain maximum CMOS integration density and HBT performance, while keeping the heterogeneous interconnect length below 5 mum.

Measurement of the electrical characteristics of 250 devices on the same 2 in. diameter wafer shows that Ti/Al/Ir/Au Ohmic contacts on AlGaN/GaN high electron mobility transistors (HEMTs) have lower average specific contact resistance after annealing at 850 °C for 30 s (4.6×10−5 Ω cm2) compared to more standard Ti/Al/Ni/Au contacts (2×10−4 Ω cm2). HEMTs with these Ir-based contacts also show average interdevice isolation currents approximately a factor of 2 lower, higher peak transconductance (134 mS/mm compared to 121 mS/mm), and higher device breakdown voltage (31 V compared to 23 V) than the devices with Ni-based contacts. This Ir-based contact metallurgy looks promising for applications requiring extended thermal stability of the HEMTs.

Ti ∕ Al ∕ Ir ∕ Au Ohmic contacts on AlGaN∕GaN high electron mobility transistors (HEMTs) show promising electrical performance, with lower specific contact resistance than obtained with the more conventional Ti∕Al∕Ni∕Au metallization. HEMTs with both types of metallization have been measured up to 550°C. We find that the dc performance of devices with Ir-based contacts is significantly better at each temperature up to this maximum value, with higher transconductance (gm), saturated drain-source current (IDSS), and more stable threshold voltage (Vth). These contacts look very promising for HEMT power amplifier applications involving high temperature operation.

We demonstrated that Sc2O3 thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, IDS, reaches a value of over 0.8 A/mm and is ∼40% higher on Sc2O3/AlGaN/GaN transistors relative to conventional HEMTs fabricated on the same wafer. The metal–oxide–semiconductor HEMTs (MOS–HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that Sc2O3 retains a low surface state density on the AlGaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to +6 V of gate voltage. In particular, Sc2O3 is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO.

AlGaN/GaN high electron mobility transistors with either MgO or Sc2O3 surface passivation were irradiated with 40 MeV protons at a dose of 5×109 cm−2. While both forward and reverse bias current were decreased in the devices as a result of decreases in channel doping and introduction of generation–recombination centers, there was no significant change observed in gate lag measurements. By sharp contrast, unpassivated devices showed significant decreases in drain current under pulsed conditions for the same proton dose. These results show the effectiveness of the oxide passivation in mitigating the effects of surface states present in the as-grown structures and also of surface traps created by the proton irradiation.

Both MgO and Sc2O3 are shown to provide low interface state densities (in the 10 11 eV -1 cm -2 range) on n-and p-GaN, making them useful for gate dielectrics for metal-oxide semiconductor(MOS) devices and also as surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs).Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of ~3 × 10 12 cm -2 . On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN structures are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy(40MeV) protons.

High electron mobility transistors (HEMTs) were fabricated from AlGaN/GaN on semi-insulating SiC substrates with excellent performance and high yield. The devices had 0.14 mum T-gates with a total width of 300 mum. Extrinsic, unpassivated peak performance values for these HEMTs include transconductance of 338 mS/mm, maximum drain current of 1481 mA/mm, unity current gain cutoff frequency of 91 GHz, and maximum frequency of oscillation of 122 GHz. Saturated CW power measurements of these devices at 10 GHz result in 4.6 W/mm with PAE at 46 % when optimized for power and 3.0 W/mm with PAE at 65 % when optimized for efficiency.

AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) on 2 in. diameter GaN buffer layers grown by hydride vapor epitaxy (HVPE) on sapphire substrates. HEMTs with 1 μm gate length displayed excellent dc and rf performance uniformity with up to 258 separate devices measured for each parameter. The drain–source saturation current was 561 mA with a standard deviation of 1.9% over the 2 in. diameter, with a corresponding transconductance of 118±3.9 mS/mm. The threshold voltage was −5.3±0.07 V. The rf performance uniformity was equally good, with an fT of 8.6±0.8 GHz and fmax of 12.8±2.5 GHz. The results show the excellent uniformity of the MBE technique for producing AlGaN/GaN HEMTs and also the ability of HVPE to provide high quality buffers at low cost.

DC current-switching and power-switching transients of various GaN-based FET structures are investigated. Two different characteristics are compared, namely, thermal and electronic transients. While the thermal transients are mainly reflected in changes in channel carrier mobility, the electronic transients are dominated by charge instabilities caused by the polar nature of the material. The discussion of the electronic transients focuses, therefore, on instabilities caused by polarization-induced image charges. Three structures are discussed, which are: 1) a conventional AlGaN/GaN heterostructure FET, 2) an InGaN-channel FET, and 3) an AlGaN/GaN double-barrier structure. In structures 2) and 3), field-induced image charges are substituted by doping impurities, eliminating this source of related instability. This is indeed observed.

A comparison was made of specific contact resistivity and morphology of Ti/Al/Pt/WSi/Ti/Au and Ti/Al/Pt/W/Ti/Au ohmic contacts to AlGaN/GaN heterostructures relative to the standard Ti/Al/Pt/Au metallization. The W- and WSi-based contacts show comparable specific resistivities to that of the standard contact on similar layer structures, reaching minimum values of ∼10−5 Ω cm2 after annealing in the range 850–900 °C. However, the W- and WSi-based contacts exhibit much smoother surface morphologies, even after 950 °C annealing. For example, the root-mean-square roughness of the Ti/Al/Pt/WSi/Ti/Au contact annealed at 950 °C was unchanged from the as-deposited values whereas the Ti/Al/Pt/Au contact shows significant deterioration of the morphology under these conditions. The improved thermal stability of the W- and WSix-based contacts is important for maintaining edge acuity during high-temperature operation.

AlGaN/GaN high electron mobility transistors are extremely promising for microwave power generation from S band up to Ka band. The list of potential applications includes commercial wireless base stations, phased array radar, satellite -based communication systems, digital radio and power flow control. Results to date show excellent power performance, with densities>10W.mm(-1) and high efficiency. In this paper we give a brief overview of the field, report on use of single-crystal oxide layers to provide effective surface passivation for HEMTs and then discuss some new spin-based GaN devices that may have a role in expanding the functionality of nitride electronics and photonics.

The rf performance of 1×200 μm2 AlGaN/GaN MOS-HEMTs with Sc2O3 used as both the gate dielectric and as a surface passivation layer is reported. A maximum fT of ∼11 GHz and fMAX of 19 GHz were obtained. The equivalent device parameters were extracted by fitting this data to obtain the transconductance, drain resistance, drain–source resistance, transfer time and gate–drain and gate–source capacitance as a function of gate voltage. The transfer time is in the order 0.5–1 ps and decreases with increasing gate voltage.

Both MgO and Sc 2 O 3 are shown to provide low interface state densities (in the 10 11 eV -1 cm -2 range) on n- and p-GaN, making them useful for surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs) and also gate dielectrics for metal-oxide semiconductor(MOS) devices. Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of ∼3 × 10 12 cm -2 . On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN diodes and Sc 2 O 3 passivated HEMT are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy(40MeV) protons.

MBE-deposited Sc/sub 2/O/sub 3/ films are found to effectively passivate surface states in the gate-drain region of AlGaN/GaN HEMTs. The effect of the passivation is observed in higher forward I/sub DS/-V/sub DS/ three-terminal breakdown voltage and output power under class A operation. In the latter case, the power-added efficiency was at least doubled.

The effect of layer structure (GaN versus AlGaN cap) and cleaning procedure prior to Sc2O3 or MgO deposition at 100 °C were examined for their effects on the long-term bias-stress stability of AlGaN/GaN high electron mobility transistors (HEMTs). Surface cleaning by itself was not sufficient to prevent current collapse in the devices. The forward and reverse gate leakage currents were decreased under most conditions upon deposition of the oxide passivation layers. After ≈13 h of bias-stressing, the MgO-passivated HEMTs retain ⩾90% their initial drain–source current. The Sc2O3-passivated devices retained ∼80% recovery of the current under the same conditions.

The low temperature (100 degreesC) deposition of Sc2O3 or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5 x 100 mum(2) HEMTs for both types of oxide passivation layers. Both Sc2O3 and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiN. passivation which typically showed <2 dB increase on the same types of devices. The, HEMT gain also in general remained linear over a wider input power range with the Sc2O3 or MgO passivation. These films appear promising for reducing the effects of surface states on the do and if performance of AlGaN/GaN HEMTs.

Three different passivation layers (SiN/sub x/, MgO and Sc/sub 2/O/sub 3/) were examined for their effectiveness in mitigating surface-state-induced current collapse in AlGaN/GaN high electron mobility transistors (HEMTs). The plasma-enhanced chemical vapor deposited SiN/sub x/ produced /spl sim/80-85% recovery of the drain-source current, independent of whether SiH/sub 4//NH/sub 3/ or SiD/sub 4//ND/sub 3/ plasma chemistries were employed. Both the Sc/sub 2/O/sub 3/ and MgO produced essentially complete recovery of the current in GaN-cap HEMT structures and /spl sim/80-95% recovery in AlGaN-cap structures. The Sc/sub 2/O/sub 3/ had superior long-term stability, with no change in HEMT behavior over 5 months aging.

Low energy electron-excited nano-luminescence (LEEN) spectroscopy has been used to correlate higher intensities of deep level emissions with higher ohmic contact values on AlGaN/GaN device layers. Deep level defect emissions in the AlGaN layers have also been identified by LEEN as a signature of uncharacteristically high sheet resistances for a given wafer. The spectral features observed locally at the ohmic contact region are compared with direct electrical measurements of the same device structures. Ohmic contacts formed by annealing Ti/Al/Ni/Au at 800 °C for 30 s in nitrogen range from 1.0×10−6 to 1.0×10−4Ωcm2 (0.2–3.9 Ωmm), with average sheet resistance values ranging from 650 to 2275 Ω/□ as Al mole fraction decreases. The depth dependent characterization capacity of LEEN allows the density of defect emissions to be assigned to particular interfaces. For these samples, the deep level emissions found at 2.20 and 2.60–3.15 eV found near the surface of the sample while the defect emissions associated with high sheet resistance are found to be in the AlGaN layer itself. Unprocessed material shows that samples with the lowest amounts of midgap luminescence produce the lowest contact resistance. This information can be used to determine the outcome of device fabrication prior to contact formation.