InGaP/GaAs pnp Heterojunction Bipolar Transistor with δ-Doped Sheet between Base-Emitter Junction

In this article, a novel InGaP/GaAs pnp δ-doped heterojunction bipolar transistor is first demonstrated. Though the valence band discontinuity at InGaP/GaAs heterojunction is relatively large, the addition of a δ-doped sheet between two spacer layers at the emitter-base junction effectively eliminates the potential spike and increases the confined barrier for electrons, simultaneously. Experimentally, a high current gain of 25 and an offset voltage of 100 mV are achieved. The offset voltage is much smaller than the conventional InGaP/GaAs pnp HBT. The proposed device could be used for linear amplifiers and low-power complementary integrated circuit applications.

Theoretical Investigation of Ultrathin Gate Dielectrics

We describe a theoretical methodology for screening potential gate dielectric materials. A recently proposed method for constructing realistic structural models of the Si-dielectric interface is used to generate the Si-SiO2-Si and Si-SiON-SiO2-Si model metal-oxide-semiconductor (MOS) structures. We discuss methods to estimate the valence band discontinuity at the corresponding interface. We use Landauer's ballistic transport approach to investigate the low bias leakage through these ultrathin dielectric layers.

p-InGaN/n-GaN Heterojunction Diodes and their Application to Heterojunction Bipolar Transistors

ABSTRACTp-InGaN/n-GaN heterojunction diodes were grown by metalorganic vapor phase epitaxy and characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements. We changed the In mole fraction in p-InGaN from 0 to 25% to investigate diode characteristics. All the diodes showed rectified I-V characteristics at room temperature. The ideality factors obtained from forward I-V characteristics were around 2, meaning that the recombination current is dominant instead of the tunneling current through the defects in depletion layers of the diodes. The breakdown voltage in reverse I-V characteristics depends on the net donor concentration (ND - NA) in n-GaN instead of the In mole fraction in p-InGaN. This result also means that the defects in p-InGaN do not influence the breakdown voltage. The built-in potential from C-V measurements decreases with the In mole fraction in p-InGaN, meaning that the valence band discontinuity increases with the In mole fraction. This valence band discontinuity realizes the hole confinement in an HBT with an p-InGaN base. Using these InGaN/GaN heterojunction diodes, an InGaN/GaN double heterojunction bipolar transistor was fabricated for the first time. The maximum current gain of 1.2 was obtained at room temperature.