The kink effect is a phenomenon that typically occurs in InP-based InAlAs/InGaAs high electron mobility transistors (HEMTs) at cryogenic temperatures. It results in higher output conductance (gDS) and non-monotonic behavior. This Letter discusses the origin and suppression of the kink effect in InP HEMTs at cryogenic temperatures, which is linked to the structure of gate recess passivation. At room temperature, two devices with different gate recess passivation structures show similar characteristics. However, a temperature-sensitive kink is observed in the non-passivated gate recess structure, leading to the discontinuous transconductance (gm) and the non-monotonic threshold voltage (Vth) shifts. Based on pulsed and static (non-pulsed) measurement data, surface traps and impact ionization in the high-field region are identified as the origin of the kink effect. Specifically, a positive Vth shift of +160 mV is caused by surface traps when the temperature drops to 150 K. A negative Vth shift of –60 mV is due to the enhanced impact ionization below 150 K. Conversely, the device with a passivated gate recess has a negligible kink effect and effectively improves discontinuous gm and the non-monotonic Vth shifts (+25 mV) when the temperature drops. Therefore, the device with a passivated gate recess is significant for suppressing the kink effect and maintaining the stability of the device in variable temperature environments.

Silicon nanocrystals (Si-NCs) were applied on the front surface of a conventional silicon solar cell. Considering absorption with multiple exciton generation (MEG) yields and consequently photoluminescence, the cell performance was simulated based on a numerical model founded on experimental results in literature. The results show that the cell efficiency could be prominently enhanced by MEG yields and spectral down-conversion. However, though MEG yields could reach 250% within Si-NCs, it only contributes 8.7% to the cell efficiency enhancement while wavelength shifting dominates the cell efficiency enhancement mechanism. Additionally, extraction factor which is defined as ratio of photons extracted from Si-NCs to the generated carries in Si-NCs is the most critical parameter for cell performance improvement. Therefore, to realize this novel structure cell, further experimental work should be lay on improving MEG efficiency as well as photoluminescence efficiency and optical confinement of the photoluminescence.

Cryogenic InP High-electron-mobility transistors (HEMTs)-based low-noise amplifiers (LNAs) have been applied in deep space exploration, which demands high performance from InP HEMTs. Specifically, at low temperatures, the device needs to achieve low power consumption and high operating frequency. In this study, we fabricated a double-recessed InP HEMT with a heavily doped In0.65Ga0.35As/In0.53Ga0.47As/In0.52Al0.48As multilayer cap structure to optimize the device’s performance at low temperatures. At low temperatures, excessive on-resistance (RON) leads to increased power dissipation and also contributes to higher noise, which affects the performance of the LNAs. We employed the heavily doped In0.65Ga0.35As layer to reduce the metal-semiconductor contact resistance, thereby effectively lowering RON. Experimental results show that at 7 K, the devices RON is 410 ٷlm, which could effectively reduce the power dissipation. Additionally, we adopted a double-recessed gate structure. This structure significantly improves the device’s maximum oscillation frequency(fmax) by reducing the parasitic capacitance. At 7 K, the device’s fmax reaches 740GHz. Furthermore, the design of the second gate recess reduces the exposed area of the gate recess, which combined with the Si3N4 passivation layer, effectively suppresses the kink effect caused by surface traps at low temperatures, further improving the device’s cryogenic performance.

Stacked structure is a good solution to overcome the low output voltage swing provided by a single device. When several devices are stacked, the bandwidth and output power are multiple times higher. This article analyzes the small‐signal voltage gain of the stacked structure, deriving the gain expression of the high‐frequency model and simplified model. Based on the specific device parameter, the different small‐signal voltage gains between the two models are compared and the designed stacked structure is proved to obtain a flat gain at low frequencies below about 3 GHz. To our best knowledge, this is the first article to analyze the gain flatness of stacked structure with two equivalent circuit models. To verify the stacked theory, a pseudomorphic high‐electron‐mobility transistor（PHEMT） power amplifier (PA) is implemented using 0.25 μm Gallium arsenide (GaAs) technology. The PA achieves an ultra‐high bandwidth of 30 MHz to 3 GHz and a linear gain of 21 dB ± 1.5 dB. At a 16‐V drain bias voltage, a saturated output power of higher than 2 W and a peak power‐added efficiency (PAE) of 44.1% are attained.

A compact nanosecond-pulse high peak power blue laser array was fabricated, achieving a peak output power of 300W using eight GaN based edge emitting lasers and stable operation without output power degradation under no active cooling. Based on theoretical equivalent circuit modeling of laser and GaN MOSFET, the effects of device capacitance and inductance on the high-current nanosecond pulsed drive signal during the switch on and off processes of nanosecond laser pulse driving were analyzed. Theoretical and experimental results verified that the kickback current is closely related to the parasitic parameters of the devices, and that suppressing parasitic inductance and increasing the current-limiting resistor in the circuit can reduce this reverse current. Furthermore, the thermal resistance of the laser was analyzed, and an aluminum nitride (AlN) ceramic heat sink was employed to lower the thermal resistance.