„True vertical GaN high speed switching transistors for direct diode laser driving”
(acronym: PioneerGaN)

Project supported by the National Centre for Research and Development under the First Polish-Berlin call for proposals.

Total cost: 3 302 052,60 PLN (including own contribution: 347 859,53 PLN)
Centre Contribution: 1 562 754,97 PLN
Duration: 01/01/2016-31/12/2018

Principal Investigator: prof. dr hab. Detlef Hommel
Project Consortium:

  1. Wrocławskie Centrum Badań EIT+ sp.  z o. o. – Consortium Leader
  2. Seen Semiconductors sp. z o. o.

The light output power of diode lasers can be significantly enhanced by electrically pulsing them in practically isothermal conditions. This allows for much higher current levels as would be acceptable for DC operation condition. Very short high current pulses are necessary in order to avoid self-heating and thermal roll-off or even destruction of the diode laser. Depending on the diode laser design, nanosecond or sub-nanosecond pulses with current levels of several tens of Amperes are required. In terms the electric circuit implementation a capacitor placed very closely to the diode laser is discharged over the laser diode by using a very fast switching transistor. Depending on the targeted current level trough the diode laser and the on-state resistor of laser and transistor the capacitor may be charged up to several hundreds of volts before being discharge. FBH has been shown already that GaN switching transistors are well suited for this purpose as they have a roughly 10-times smaller output capacitance Coss as comparable Si based devices and good high voltage blocking capabilities. Nevertheless, severe limitations for further exploiting this approach are faced by the observation that current switching speed significantly decreases with increasing current level. This is caused by the inductive loop between diode laser, switching transistor and capacitor. It limits the minimum possible switching speed of the transistor would not be a limitation. The larger the area of the loop, the larger is the effect. The minimum loop area that is possible is given by the geometrical dimensions of diode laser, GaN-transistor and capacitor which normally have to be arranged side-by-side on a printed circuit board.