The authors review recent demonstrations of improved mid-IR laser performan
ce when a type II 'W-well' structure is incorporated into the active region
. The W configuration consists of a hole quantum well (e.g. GaSb or GaInSb)
between electron quantum wells (e.g. InAs) in order to maximise the gain w
hile suppressing nonradiative Auger losses. Optically pumped W lasers recen
tly produced more than 1.4 W per facet peak power for pulsed operation at 3
00 K. An interband cascade laser with a W active region (W-ICL) has operate
d up to 286 K. The first III-V mid-IR VCSEL (lambda = 2.9 mu m) with a W ac
tive region has lased up to 280 K for pulsed operation and to 160 K for cw,
with a cw threshold of only 4 mW for a 6 mu m spot at 78 K.