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SiO 2 layers were deposited on p-GaN (hole concentration 9×1017 cm−3) by inductively coupled plasma chemical vapor deposition using an O17-enriched O2 precursor. The samples were then annealed at 500–900 °C and the SiO2 was removed. Secondary ion mass spectrometry profiling showed significant indiffusion of O17 into the GaN under these conditions, with an incorporation depth of ∼0.18 μm after the 900 °C anneal. The O17 diffusion profiles indicate that the high dislocation density in the GaN strongly affects the effective penetration depth. The GaN remained p type upon incorporation of the oxygen.

Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V~~) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, RON, was 6mQ.cm2 and 0.8Llcmz, respectively, producing figure-of-merit values for (VRB)2/RoN in the range 5-48 MW.cm-2. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of thk contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates.On-state voltages were 3.5V for the 550V diodes and 215 for the 2kV diodes. Reverse recovery times were <0.2ysec for devices switched from a forward current density of -500A.cm-2 to a reverse bias of 100V. DISCLAIMER

A GaN/AIGaN heterojunction bipolar transistor structure with Mg doping in the base and Si doping in the emitter and collector regions was grown by Metal Organic Chemical Vapor Deposition on c-axis A1203. Secondary Ion Mass Spectrometry measurements showed no increase in the 0 concentration ( 2 -3~1 0 '~ ~m -~) in the AlGaN emitter and fairly low levels of C (-4-5~10'~ cm-3) throughout the structure. Due to the non-ohmic behavior of the base contact at room temperature, the current gain of large area (-90 pm diameter) devices was <3. Increasing the device operating temperature led to higher ionization fractions of the Mg acceptors in the base, and current gains of -10 were obtained at 300 OC. 1There is a strong interest in GaN-based electronics for applications involving high temperature or high power operation, based on the excellent transport properties of the III-nitride materials system.(*-7' Impressive advances in the performance of AlGaN/GaN high electron mobility transistors continue to be reported, due to in part to the formation of piezoelectrically-induced carriers in a 2-dimensional electron gas at the There is also interest in the development of GaN/AIGaN In this letter we report on the growth by MOCVD of a graded emitter HBT structure, DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document.Spectrometry (SIMS) since these could potentially have a strong influence on device performance, and finally on the dc characteristics of HBTs fabricated on this material.The layer structure is shown schematically in Figure 1, and was grown at -1050 "C following deposition of the GaN buffer at -550 "C on the c-plane A1203 substrate. The growth system has been described in detail previously,'2o' but in brief is a rotating (1200 rpm) disk MOCVD reactor. Ammonia (NH3), trimethylgallium (TMGa) and trimethylaluminum (TMAl) were used as precursors, while silane (SiH4) and biscyclopentadienyl-magnesium (CpzMg) were employed for n-and p-type doping, respectively. High purity H2 was used as the carrier gas. After growth the sample was annealed in the reactor at 850 "C for 20 min under 140 Torr of flowing N2 to activate the Mg acceptors.There are two important aspects to dopant and background impurity control in HBT structures. The first is that the p-type dopant should be confined to the base region, and not spill-over into the adjacent n-type emitter, where it could cause displacement of the junction and hence the loss of the advantage of the heterostructure. Figure 2 shows SIMS profiles of the A1 marker, signifying the position of AlGaN emitter layer, and also the Mg doping profile in the adjacent base layer. It is clear that the reactor memory effect for Cp2Mg has produced incorporation of Mg in the emitter, although the real situation is not quite as severe as it seems in the data because of "carry-over" of the matrix A1 signal during the depth profiling. The fact that working HBTs can still be made on this material is due...

A variety of different plasma chemistries, including SF6, Clz, IC1 and IBr, have been examined for dry etching of 6H-Sic in high ion density plasma tools (Inductively Coupled Plasma and Electron Cyclotron Resonance). Rates up to 4,500A-min-' were obtained for SF6 plasmas, while much lower rates (G300A.min") were achieved with C12, IC1 and IBr. The FZbased chemistries have poor selectivity for Sic over photoresist masks (typically 0.4-0.5), but Ni masks are more robust, and allow etch depths 2 1 0 p in the SIC. A micromachining process (sequential etch/deposition steps) designed for Si produces relatively low etch rates (<2,000A.min*') for Sic.