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Critical nitride-based p-n junction issues relating to wide bandgap bipolar device performance include minority carrier lifetime, defect related current characteristics and ohmic contact properties. Recent developments in p-GaN deposition processes resulted in GaN p-i-n UV photodetectors with improved deep UV responsivity, visible light rejection and shunt resistance characteristics. From the device data, the electron diffusion length in p-GaN doped at 1·1018 cm−3 was estimated to be 790 A, and the minority carrier lifetime in the p-GaN was estimated to be 24 ps to 0.24 ns. Improved junction electrical characteristics were achieved using MBE deposition on GaN buffers grown by MOCVD. NiAu ohmic contacts were also made to p-GaN with specific contact resistances less than 10−4 Ω·cm2.

We report on the performance of AlGaN/GaN MODFETs grown by MBE. A record value of 410 V maximum drain voltage was measured for devices with current densities of 200 mA/mm. From the dependence of breakdown voltage with gate-drain separation a breakdown field of ≈1 MV/cm is estimated.

A linear motion Ga source has been constructed and tested for smooth flux variation. The beam flux can be monitored by sensors such as atomic absorption, RHEED, and pyrometric interferometry. We demonstrated stable and reproducible operation of the source using sensor feedback. Constant layer composition can be maintained despite Ga thermal desorption at high temperatures. Arbitrary composition profile can be easily achieved for band gap engineering.

In-situ cathodoluminescence (CL) is presented as a technique for determining film composition, optical quality, doping levels, and temperature of MBE grown group III nitride films. Excitation of the films is done with either the Auger or RHEED electron gun operating between 1 and 10 keV. The CL emission is monitored using a 3 nm resolution monochromator. Optimization of the GaN growth process using a RF atomic nitrogen plasma source is discussed using in-situ cathodoluminescence to reduce the yellow defect level present in GaN. Composition and quality of Al x Ga 1-x N films are shown to be quickly determined from the peak position and width. This is extremely useful in the nitride system where reflection high-energy electron diffraction (RHEED) oscillations are not routinely observed. Measurement of the substrate temperature during GaN growth is demonstrated by monitoring the shift in band edge position with temperature. p-type doping and MQW levels observed by CL are shown to allow quick optimization of device and material properties.

Homo- and heterojunction III-N light emitting diodes using RF atomic nitrogen plasma molecular beam epitaxy have been grown. GaN films deposited on sapphire using this growth technique exhibited an extremely sharp X-ray diffraction with a full width half maximum of 112 arc sec. p-type doping of the nitride films was done with elemental Mg and resulted in as-grown p-type material with resistivities as low as 2 Ω · cm. Both homo- and heterojunction LEDs showed clear rectification. Emission from the GaN homojunction deposited on n-type SiC was peaked at 410 nm while the AlGaNGaN(Zn)AlGaN double heterojunction LEDs emission was centered about 520 nm.

The group III nitrides have attracted increasing interest because of their significant potential in optoelectronics such as blue emitter and high temperature electronics. In order to take advantage of bandgap engineering of heterostructures such as GaN/AlN, a controllable growth technique is highly desired. The growth of group III nitrides by MBE (molecular beam epitaxy) requires using energetic nitrogen species which can be generated by techniques such as ion, RF (radio-frequency) and ECR (electron cyclotron resonance) sources. We report nitride results using an RF source to achieve epitaxy on sapphire. The nitrogen flux has been carefully characterized and related to the GaN quality. Schottky diode and ultra-violet (UV) photo-response are also reported.

Strained layer InAs/GaInSb superlattices have been shown to have many desirable optical and transport properties. The piezoelectric field along the (111) orientation causes a tilting of the energy bands, leading to novel opto-electronic applications. We have carried out the growth of these superlattices on (111) on- and off-axis GaSb substrates. A wide range of growth conditions has been investigated, and high-quality superlattices are demonstrated in a narrow temperature and flux range, as monitored by reflection high-energy electron diffraction (RHEED) reconstruction and post-growth X-ray diffraction analysis.

The paper describes the evaluation of devices using "locked-down" VCSEL fabrication process, which includes a more optimal growth condition for the InGaAsN-based active region. From preliminary reliability studies, product requirements, and device performance, designed stress conditions for all the reliability endurance tests are described.

Reports a selective dry-etching technique for GaAs MESFET gate recessing, where a thin AlGaAs etch stop is used to precisely control the recess depth. Selective dry etching was achieved by using a CCl/sub 2/F/sub 2//He gas mixture yielding a selectivity of >600 for GaAs over AlGaAs. A thin (35-50-AA) Al/sub x/Ga/sub 1-x/As layer (x=0.3) was used to control the etch depth. The surface composition of the RIE (reactive ion etch) recessed AlGaAs layers was analyzed by angle-resolved X-ray photospectrometry and compared to the surface compositions of the wet-chemically recessed samples. The standard deviation of MESFET threshold voltage was as low as 20 mV across a 3-in. wafer by using this selective dry-etch technique. The MESFETs show excellent electrical characteristics with transconductance of 150 mS/mm for a 1*100 mu m gate and breakdown voltages as high as 38 V. >

The design and fabrication of 0.25- mu m MESFETs with a channel length of 2.3 mu m is reported. A comparison of the effect of the FET geometry ( pi and parallel gate structures) on device performance is described. MESFETs were fabricated using a hybrid optical/e-beam lithography process on active layers grown by MBE. FETs show a transconductance of 260 mS/mm and a threshold voltage of -3.0 V. No short-channel effects were observed. From RF measurements, an f/sub max/ of 90-120 GHz was obtained. Excellent device yield across a 3-in wafer and wafer to wafer was achieved. >

Current-voltage and initial RF measurements are presented on a double-heterojunction HEMT (high-electron-mobility transistor) structure designed for power MMIC applications. The device structure is grown by molecular-beam epitaxy and uses a spatially variant superlattice to improve the performance of the inverted AlGaAs/GaAs interface. Gate recessing is achieved using a hybrid wet-chemical selective dry etching process. For selective dry etching, reactive ion etching with a >600:1 selectivity for GaAs over AlGaAs is used to control the recess depth. The room temperature DC characteristics for a 3-mm power FET (0.7- mu m gate) display an I/sub dss/ of 370 mA/mm, a peak transconductance of 180 mS/mm, and a maximum gate-to-drain breakdown of 22 V. Large-signal microwave measurements at 5.5 GHz yielded a saturated output power of 1.3 W (31.2 dBm), 8.3-dB large-signal gain, and a peak power-added efficiency of 55%. >