D.M. Keogh

Graded-base InGaN∕GaN heterojunction bipolar light-emitting transistors

The authors report radiative recombination from a graded-base InGaN∕GaN heterojunction bipolar transistor (HBT) grown by metal-organic chemical vapor deposition on sapphire. For a device with a 40×40μm2 emitter area, a differential dc current gain of 15 is measured from the common-emitter current-voltage characteristics, with the HBT breakdown voltage BVCEO>65V. The heterojunction bipolar light-emitting transistor exhibits a base-region recombination radiation peak in the visible spectral range with a dominant peak at λ=385nm (blue emission).

Device operation of InGaN heterojunction bipolar transistors with a graded emitter-base design

The device operation of InGaN heterojunction bipolar transistors with a graded InGaN emitter-base design grown by metal organic chemical vapor deposition on sapphire substrates is demonstrated. The Gummel plot, current gain, and common-emitter current-voltage characteristics of the device are presented. The dc common-emitter current gain of a 25×25μm2 (emitter size) device increases with collector current and the current gain reaches a high value of 13 at IC=10mA with a base width of 100nm and a hole concentration of p=2×1018cm−3. The improved device performance is attributed to the graded emitter-base design as well as the high quality of the material made possible by the indium composition grading that enables the epitaxial growth of InGaN layers with a low density of pits or defects. The results demonstrate the potential of the graded InGaN emitter-base junction design in nitride heterojunction bipolar transistors.