|Click on photo to enlarge.|
GaAsFETs have really become ubiquitus in every situation one wants high gain and low noise figure in frequencies ranging from the low VHF to microwaves. The picture on the left is of a very popular transistor (although a bit dated now), the ATF 10136 from Agilent Technologies. The ceramic cap has been removed to take this photo (about 200X magnification).
The chip is in the center, attached to the source strip. The diameter of the white ceramic material is about 1.5 mm. The drain is on the right and the gate on the left. Observe the thin gold wires that connect the chip to its carrier contacts (and to your circuits!). This particular transistor (from a low-noise 2-m preamp) had a cruel death: it was accidentally (and quite scandalously!) bombarded with high power on 144 MHz from the amplifier of an EME setup in a friend's station. The gate short-circuited to the source, and you may see that even the gold wires almost melted by the heavy current that destroyed the transistor (see the red arrow). Fortunately, nowadays those great transistors are fairly cheap to replace, and can be easily procured. Thumbs up to Agilent (now Avago, and the other semiconductor manufacturers) that make our beloved toys!