Optoelectronic Phenomena in Heterostructures Laboratory

Background
Photoconductive semiconductor switches (PCSS's) based on bulk semi-insulating (SI) wafers are widely used for high power pulsed systems such as ultra-wide band impulse radars, high power pulsed lasers, and high power microwave and millimeter-wave systems. Among well-known PCSS devices, gallium arsenide PCSS's have recently attracted considerable attention because of their high sensitivity to optical triggering. Compare to the widely used high power device material, which is silicon, GaAs/AlGaAs material provides opto-electonic transmission inside the device structure. This principal novel feature opens new opportunities for engineering design.

Description
The baseline switch technology have been directed towards the reproducible fabrication of gallium arsenide high-voltage (HV) switches with switching speed is much faster than that of conventional silicon three-electrode pulse switches. Within the three-electrode semiconductor's switches the Photon Injection Pulsed Switches (PIPS) with the internal optical coupling between p-n junctions demonstrate phenomenal results in its dynamic and output characteristics (Table 1). The HV switches are made by LPE (Liquid Phase Epitaxy) technology on the base of GaAs and relative materials.

Fig. 1. Photon Injection Pulsed Switch (PIPS)

Switches Features (see also Table 2 and Figure 2)
- Subnanosecond Rise Time of Pulses
- High Reliability with High Terma and Radiation Specifications
- Picoseconds Stability vs triggering current
- High Pulse Power Output with Low Energy Losses
- Nanoseconds Delay Time

Application Positioning and comparable characteristics
Table 3 compares profiles of the High Speed Pulse and Impulse Generators made by world leading manufacturers. Various applications of these devices scope from high speed analyzers and triggering systems to measurement devices of the flight time in mass spectroscopy and EMP simulation. It is seen that the generators based on GaAs PIPS are able to produce pulses in wide scope of pulse duration including extremely short down to 0.5 ns. That can be used in ultra-wide band impulse radar systems.
Tables 4 and 5 show characteristics of generators used in high-speed Pulse Laser Diode Drivers. These generators are combined with high power pulsed laser systems to measure the flight time returned from a physical object, to measure distance, speed and acceleration of the object. Typical applications of the systems include laser rangefinders, position sensors, motion sensors, designators, and communications. The exceptional performance of the PIPS technology makes it possible to provide both high range resolution by modulation of ultrashort optical pulse width (Table 4) and desirable output optical power by high current amplitude (Table 5).

It is seen from the tables that the generators based on GaAs PIPS have some remarkable advantages for the market needs:
- pulsers based on GaAs PIPS are able to commute both high voltage and high current amplitude pulses
- pulsers based on GaAs PIPS are able to generate pulses with subnanosecond rise and fall times
- pulsers based on GaAs PIPS have high PRF compare to other high voltage and high power drivers

Note: The limited characteristics of working PIPS depend very much on each others. For instance, the higher the current is required the lower the pulse duration and pulse repetition frequency are to be provided to prevent device overheating. Also the higher the current the longer the rise time and longer the jitter. Thus, in practice (in the generator units) all these aggregated PIPS parameters (see below) are to be taken into account.

Fig. 2. Typical GFT modulators output voltage pulse form