Insufficient hole injection is a major impediment to the luminescence efficiency of III-nitride light-emitting diodes (LEDs). In our previous work by Zhang et al. [Appl. Phys. Lett. 97, 062103 (2010)], high-density mobile three-dimensional hole gas is obtained in Mg-doped Al composition graded AlGaN layer with Al composition linearly decreasing from a certain value to 0. In this paper, it is revealed by a theoretical study that the hole injection efficiency in blue-light GaN-based LEDs can be greatly enhanced by using this polarization-doped method. An increase in the electroluminescence intensity and the internal quantum efficiency in polarization-doped GaN-based LEDs is observed, in comparison with a conventional LED.

We report AlGaN/GaN n-p-n heterojunction bipolar transistors (HBTs) on sapphire substrates with selective-area grown AlGaN emitters by metal-organic chemical vapor deposition. Metal-semiconductor contact on the external p-GaN base layer shows ohmic characteristics thanks to the dry-etching-free process of base- emitter junction. As a result, the maximum current gain β is around 90 calculated from the Gummel plot of a 20×20 μm ² HBT device. Common-emitter I-V family curves exhibit offset voltage (V _offset ) <; 0.5 V and knee voltage (V _knee ) <; 6.5 V. A high current density JC of 8 kA/cm ² and power density of 75 kW/cm ² were obtained. These values are the highest in the reported for GaN-based HBTs on sapphire substrates. The open-base breakdown voltage (BV _CEO ) exceeds 98 V comparable with direct-growth GaN-based HBTs.

N-p-n AlGaN/GaN heterojunction bipolar transistors (HBTs) on sapphire substrates with high current gain $\beta $ of 129, low specific ON-resistance ( $\textit{R}_{\biosc{on},\text{sp}}\text{)}$ of 0.28 m $\sf\Omega \cdot$ cm $^{\text{2}}$ and high current density $\textit{J}_{\textit{C}}$ of $\sim$ 15 kA/cm $^{\text{2}}$ (if normalized to emitter area, $\textit{R}_{\biosc{on},\text{sp}} \sim$ 0.15 m $\sf\Omega \cdot$ m $^{\text{2}}$ and $\textit{J}_{\textit{C}} \sim$ 28.4 kA/cm $^{\text{2}}\text{)}$ have been demonstrated. The analysis of component of $\textit{R}_{\biosc{on},\text{sp}}$ yields the collector resistance is $\sim$ 5.2% of the total $\textit{R}_{\biosc{on},\text{sp}}$ , showing the low ON-resistance advantage of GaN HBTs. The open-base avalanche breakdown voltage (BV $_{\text{CEO}}\text{)}$ is $\sim$ 160 V. High-temperature performance of GaN HBT is also evaluated. The $\textit{R}_{\biosc{on},\text{sp}}$ is reduced as temperature increasing in the range of 25 $^{\circ}$ C–100 $^{\circ}$ C due to enhanced hole concentration in the base layer. The cutoff frequency ( $\textit{f}_{\textit{T}}\text{)}$ of greater than 4 GHz is determined at $\textit{V}_{\text{CE}} =$ 9 V. These results dominate that GaN HBTs have been anticipated to become a new technology for next-generation power switches and RF power amplifier circuit.

In this brief, a scaled In $_{{0}.{17}}$ Al $_{{0}.{83}}\text{N}$ /GaN high-electron-mobility transistor (HEMT) was fabricated on sapphire substrate with 47-nm ${T}$ -gate length, 300-nm source–drain distance, and selective area regrown $\text{n}^{+}$ -GaN. The device exhibits cutoff frequencies ${f}_{\text {T}}/{f}_{\text {max}}$ of 190/301 GHz, which gives a record sqrt ( ${f}_{\text {T}} \times {f}_{\text {max}}{)}$ = 239 GHz among reported Ga-polar GaN-on-sapphire HEMTs. The device shows a maximum current density, a peak external direct current transconductance, and an ${I}_{\text {on}}/{I}_{\text {off}}$ ratio of 1.45 A/mm, 610 mS/mm, and $2.9\times 10^{6}$ , respectively. Drain-induced barrier lowering of 75 mV/V is measured at ${I}_{\text {ds}}$ = 1 mA/mm between ${V}_{\text {ds}}$ = 1 V and 5 V. The three-terminal OFF-state breakdown voltage is 14.7 V. The effective electron velocity of the 2-D electron gas (2DEG) under the gate foot is estimated to be $1.4\times 10^{7}$ cm/s. These characteristics of this Ga-polar millimeter wave (mm-wave) GaN-on-sapphire HEMT are comparable with those state-of-the-art counterparts on SiC substrates.

The selective-area regrowth (SAG) n-type GaN source/drain electrode has been widely used in high electron mobility transistors (HEMTs) for high-frequency applications. Previous studies focused only on device performances, but not on SAG n⁺-GaN in devices. This paper studies electron concentration and mobility of SAG n⁺-GaN on InAlN/GaN HEMTs via metal-organic chemical vapor deposition (MOCVD). It is revealed that electron mobility of SAG GaN is significantly affected by thickness. The decrease in mobility in a thin GaN may be attributed to regrowth interface defects. A gas flow model on the regrowth region is proposed to guide the regrowth of SAG GaN for improving the electron mobility. A high electron mobility of 138 cm²/V s with an electron concentration of 5.2 × 10¹⁹/cm³ is obtained from an 80-nm n⁺-GaN with the regrowth width of 10 μm. Due to the high doping level, the nonalloy metal-semiconductor contact resistance (R_m-GaN) is as low as 0.041 Ω mm. The interface resistance (R_int) between GaN and 2DEG is extracted using transfer length measurement (TLM) models and found to be 0.106 Ω mm. The on-resistance (R_on) is 0.753 Ω mm for InAlN/GaN HEMT with a source-drain metal spacing (L_{sd metal}) of 2 μm.

AlGaN/GaN E/D-mode GaN inverters are successfully fabricated on a 150-mm Si wafer. P-GaN gate technology is applied to be compatible with the commercial E-mode GaN power device technology platform and a systematic study of E/D-mode GaN inverters has been conducted with detail. The key electrical characters have been analyzed from room temperature (RT) to 200 °C. Small variations of the inverters are observed at different temperatures. The logic swing voltage of 2.91 V and 2.89 V are observed at RT and 200 °C at a supply voltage of 3 V. Correspondingly, low/high input noise margins of 0.78 V/1.67 V and 0.68 V/1.72 V are observed at RT and 200 °C. The inverters also demonstrate small rising edge time of the output signal. The results show great potential for GaN smart power integrated circuit (IC) application.