Search

Using InP/InGaAs layers grown by metal organic molecular beam epitaxy (MOMBE) on semi-insulating (SI) InP substrate we have fabricated waveguide-integrated pin-photodiodes working on the principle of evanescent field coupling. A 3dB cutoff frequency of 9.6 GHz has been found in a 50 Ω system. The 100 μm long diodes exhibit a capacitance of < 0.1 pF at −5 V bias. In addition design criteria are given to improve the speed of the devices.

Monolithic arrays of four InP/lnGaAs pin photodiodes for wavelength division multiplexing applications have been fabricated on semi-insulating InP substrate. The diodes have a diameter of 30 μm on a 60 μm pitch. Deep trenches are used to isolate the individual diodes from each other. A crosstalk below −30 dB is achieved for frequencies up to about 3.3 GHz. Pulse measurements at the individual diodes show a falltime of 33 ps corresponding to a 3dB bandwidth in excess of 10 GHz.

It is shown that strained isoelectronically doped buffer layers grown on GaAs and InP substrates allow one to reduce the dislocation density as well as the deep level concentration. Photoluminescence measurements show an improved near gap luminescence and a reduced deep level emission. This has been also confirmed by DLTS measurements. The higher material quality is also reflected in the device performance. GaAs Schottky diodes (n ˜0.5 · 1016Cm-3) exhibit a leakage current of 100 pA up to 50 V reverse bias at room temperature even with large Schottky contact area of 125 μm × 60 μm. This technique allows the quality of electronic and optoelectronic devices to be improved.

On p-type Ga 0.47 In 0.53 As LPE-grown layers, Schottky diodes were fabricated with different metals and surface preparations. On chemically etched surfaces, diodes with ideality factors near unity but rather low breakdown voltages with soft breakdown were achieved. The barrier heights were between 0.4 and 0.7 eV depending on the work function of the metal. On sputter-cleaned surfaces the diodes exhibited high breakdown voltages and barrier heights of about 0.7 eV independent of the metal. Annealing of the diodes at 320°C resulted in reduced series resistances and barrier heights in the case of sputteretched surfaces. The junction seems to consist of two different barriers; the lower one is determined by an As segregation at the interface, whereas the higher one is caused by traps which are induced by the sputter process.

A two-step liquid-phase-epitaxial process has been used to fabricate widegap-emitter Schottky collector transistors. After the growth of the first two epitaxial layers the sample has been structured and then overgrown in a second run. In that way a pn homojunction in the widegap material (InP) underneath the extrinsic base-emitter region and a pn heterojunction under the collector have been formed. First transistors fabricated show a current gain of 10 in the common-emitter configuration.

A Schottky contact photodiode on p-type GaInAs for application at λ=1.3–1.6 μm has been fabricated and tested. The coaxial type device shows an external quantum efficiency of 19% at λ=1.27 μm, and rise and fall times of less than 15 ps.

In the InP/GaInAs material system heterojunction bipolar transistors have been fabricated on isoelectronically doped InP buffer layers. The greatly improved performance of the B?E diodes, especially at low forward bias, is reflected in the improved behaviour of bipolar transistors.

A widegap-emitter transistor with a Schottky collector has been fabricated using n-InP as the emitter, p-GaInAs as the base layer and Ni as the Schottky metallisation. The fabricated transistors show a current gain better than 5 in the common-emitter configuration.