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Results are presented on a lateral current injection vertical cavity surface emitting laser (VCSEL) structure, the implant apertured, index guided VCSEL (I 2 -VCSEL). This approach was previously used for 980 nm emission and has now been adapted for 850 nm emission. The threshold current is as low as 0.8 mA for 7 μm diameter current apertures. Typical slope efficiencies of 0.45–0.5 mA/mW are obtained for output mirror reflectivity of 99.5%. Small-signal measurements of the modulation response indicate instrument-limited bandwidths in excess of 11 GHz. Large-signal measurements demonstrate 10 Gb/s operation with bit-error rates below 10 −13 . In addition, high repetition rate pulses were generated by gain switching both single and multimode VCSELs. These Gaussian pulses had time bandwidth products below 2.5, pulse widths as low as 29.6 ps and timing jitter as low as 5.5 ps.

The development of a self-aligned fabrication process for small emitter contact area ( 2×4 μ m2) GaN/AlGaN heterojunction bipolar transistors and GaN bipolar junction transistors is described. The process features dielectric-spacer sidewalls, low damage dry etching and selected-area regrowth of p-GaAs(C) on the base contact or n-GaN/AlGaN on the emitter contact. Series resistance effects are still found to influence the device performance.

Low resistance ohmic contacts are difficult to form on p-type GaN and AlGaN due to the relatively high ionization energy of Mg in GaN and AlGaN. A carbon-doped GaAs grown on p-GaN prior to ohmic metallization has been shown to improve contact resistance to p-GaN. npn AlGaN/GaN heterojunction bipolar transistors and GaN bipolar junction transistors have been demonstrated by employing a regrowth C-doped GaAs to the p-GaN base regions. GaN/AlGaN epilayers were grown with a molecular beam epitaxy system and C-doped GaAs (1020 cm−3) was regrown on the devices (∼500 A) by metal organic chemical vapor deposition using SiO2 as mask. Very high current densities were achieved for common base operation in both device types and devices were operable at 250°C.

Heavily carbon-doped (p≥10 10 cm −3 ) GaAs layers were grown on p-GaN in attempt to reduce the p-ohmic contact resistance. While the specific contact resistances on the p-GaN and p-GaAs were typical of the current state-of-the-art (∼10 −3 and 10 −5 Ω cm 3 , respectively), the high valence band offset at the GaAs/GaN interface produced a barrier to hole transport. The specific contact resistance for the GaAs(C)/GaN(Mg) structure was better than that of GaN alone, but was still in the 10 −3 Ω cm 2 range, even after alloying of the metal at 800°C. Other approaches to lowering contact resistance on p-GaN are discussed.

Selective etching of GaAs over AlGaAs and InGaP was examined in different plasma chemistries (BCl3/SF6, BCl3/NF3, IBr, ICl, BI3, and BBr3) in a high density plasma reactor. The normal etch stop reactions involving formation of involatile AlF3, InF3, or InCl3 are found to be less effective under high density conditions because of the higher ion-assisted etch product desorption efficiency. Addition of SF6 to BCl3 produces higher selectivities than NF3 as an additive, while IBr, ICl and BBr3 are essentially non-selective for both heterostructure systems. Selective etching of InGaP over GaAs is achieved using the BI3 chemistry.

A parametric study of etch rates and surface morphologies of In-containing compound semiconductors (InP, InGaAs, InGaAsP, InAs and AlInAs) obtained by BClj-based Inductively Coupled Plasmas is reported. Etch rates in the range 1,500-3,000 &min. are obtained for all the materials at moderate source powers (500 W), with the rates being a strong function of discharge composition, rf chuck power and pressure. Typical root-mean-square surface roughness of-5 nm were obtained for InP, which is worse than the values obtained for Ga-based materials under the same conditions (-1 run). The near surface of etched samples is typically slightly deficient in the group V element, but the depth of this deficiency is small (a few tens of angstroms).

Inductively coupled plasma (ICP) etching of all of the main III–V compound semiconductors is reported as a function of source and chuck power, pressure and gas additive (Ar, N2, H2) in Cl2 plasmas. Etch rates between 2000 and 5000 A min−1 were obtained for all materials at moderate source power (750 W) and low d.c. self-bias (≤ −150 V). Surface morphologies were smooth over a broad range of conditions for Ga-based materials, while for In-based semiconductors there was a much narrower window of appropriate ion-to-neutral ratios to obtain smooth etched surfaces on In-based semiconductors.

High ion density plasma conditions are found to create severe reductions in carrier density and reduction in photoluminescence intensity in doped AlGaAs and InGaP during exposure to Electron Cyclotron Resonance SF6 discharges. These are typical of processes where SiNx or SiO2 are removed from an underlying semiconductor layer, and suggest that conventional reactive ion etching, or alternatively low power or high pressure ECR conditions are necessary to avoid ion-induced damage.

The etch rates of InGaP, AlInP and AlGaP are more than an order of magnitude larger in microwave-enhanced BCl3/Ar discharges relative to conventional reactive ion etch (RIE) conditions. This is due to the increased atomic radical and ion densities. While RIE discharges produce rough, non-stoichiometric surfaces of InGaP and AlInP due to the formation of an InCl3 selvedge layer, the surfaces of samples etched under ECR conditions are generally smooth and stoichiometric. This difference is found to be due to the efficient ion-assisted desorption of InCl3 under high ion density conditions. The advantage of this process is that simple BCl3-based plasma chemistries can be employed for all III–V semiconductors, whereas previously CH4/H2 was used for In-containing materials and chlorine chemistries for Ga-containing materials. The etch rate of AlGaP is substantially slower than the other two materials, which can be explained on the basis of the bonding differences.

Red emission at 621 nm from the 5 D 0 → 7 F 2 transition of Eu +3 has been obtained from GaN:Eu grown by gas-source molecular beam epitaxy. The luminescence has been found to be more intense than the red emission from metalorganic chemical vapor deposition (MOCVD) derived AlGaAs. Upon annealing in both N 2 and N 2 /H 2 mixtures up to 800°C, the integrated photoluminescence (PL) intensity was found to remain within a factor of 2 of the as grown sample. The surface morphology also remained unchanged. Thermal quenching measurements of the as-grown sample saw a reduction in the 621 nm emission of 82% as the measurement temperature was increased from 20 to 300 K. The quenching was reduced to 66% after annealing at 800°C.

We report the demonstration of both enhancement-mode p - and n -channel GaAs metal oxide semiconductor field effect transistors (MOSFETs) on GaAs semi-insulating substrates using high quality Ga 2 O 3 (Gd 2 O 3 ) as the gate dielectric and the conventional ion-implant technology. The source and drain regions were selectively implanted with Zn or Si for low resistance ohmic contacts for p - or n -MOSFETs, respectively. AuBe/Pt/Au, Ge/Mo/Au-Ge/Mo/Au, and Ti/Pt/Au were deposited for p - and n -ohmic contacts and gate electrode, respectively. The devices, with a 4 × 50 μ m 2 gate geometry, exhibit an extrinsic transconductance of 0.18 and 0.1 mS/mm for p - and n -MOSFETs, respectively, and an excellent gate breakdown field greater than 3 MV cm −1 .