Hui Nie

27.6% Conversion efficiency, a new record for single-junction solar cells under 1 sun illumination

Alta Devices, Inc. has fabricated a thin-film GaAs device on a flexible substrate with an independently-confirmed solar energy conversion efficiency of 27.6%, under AM1.5G solar illumination at 1 sun intensity. This represents a new record for single-junction devices under non-concentrated sunlight. This surpasses the previous record, for conversion efficiency of a single-junction device under non-concentrated light, by more than 1%. This is due largely to the high open-circuit voltage (Voc) of this device. The high Voc results from precise control of the dark current. The fact that this record result has been achieved with a thin-film shows that, for GaAs material systems, the majority of the growth substrate is not needed for device performance. This allows one to consider amortizing the potentially high cost of a GaAs growth substrate by growing a thin-film, lifting it off, and reusing the same substrate multiple times. This technology therefore has the potential to be a novel high-performance, thin-film option for terrestrial photovoltaics.

1.5-kV and 2.2-m \(\Omega \) -cm \(^{2}\) Vertical GaN Transistors on Bulk-GaN Substrates

In this letter, vertical GaN transistors fabricated on bulk GaN substrates are discussed. A threshold voltage of 0.5 V and saturation current >2.3 A are demonstrated. The measured devices show breakdown voltages of 1.5 kV and specific ON-resistance of 2.2 mΩ-cm 2 , which translates to a figure-of-merit of V BR 2 /R ON ~1 × 10 9 V 2 Ω -1 · cm -2 .

High Voltage Vertical GaN p-n Diodes With Avalanche Capability

In this paper, vertical p-n diodes fabricated on pseudobulk gallium nitride (GaN) substrates are discussed. The measured devices demonstrate breakdown voltages of 2600 V with a differential specific on-resistance of 2 mΩ cm2. This performance places these structures beyond the SiC theoretical limit on the power device figure of merit chart. Contrary to common belief, GaN devices do possess avalanche capability. The temperature coefficient of the breakdown voltage is positive, showing that the breakdown is indeed because of impact ionization and avalanche. This is an important property of the device for operation in inductive switching environments. Critical electric field and mobility parameters for epitaxial GaN layers grown on bulk GaN are extracted from electrical measurements. The reverse recovery time of the vertical GaN p-n diode is not discernible because it is limited by capacitance rather than minority carrier storage, and because of this its switching performance exceeds the highest speed silicon diode.

3.7 kV Vertical GaN PN Diodes

There is a great interest in wide band-gap semiconductor devices for power electronics application. In this letter, vertical GaN p-n diodes fabricated on bulk GaN substrates are discussed. The device layers are grown by MOCVD on low defect density (104 cm-2) bulk GaN substrates. The measured devices show breakdown voltages of 3.7 kV with an area differential specific on-resistance (Rsp) of 2.95 mΩ-cm2.

Vertical power diodes in bulk GaN

Vertical diodes with breakdown voltages up to 2.6kV have been fabricated on bulk GaN substrates. The measured figures-of-merit of these devices show performance near the theoretical limit of GaN. These vertical GaN diodes exhibit robust avalanche breakdown behavior with a positive temperature coefficient. System-level performance advantages have been demonstrated in power conversion applications. Statistical data have been collected from thousands of devices. Initial reliability tests have been completed.

400-A (Pulsed) Vertical GaN p-n Diode With Breakdown Voltage of 700 V

There is a great interest in monolithic GaN semiconductor devices with high current capability for power electronics. In this letter, large area vertical GaN p-n diodes fabricated on bulk GaN substrates are discussed. Diodes with areas as large as 16 mm2 with breakdown voltages exceeding 700 V and pulsed (100 μs) currents approaching 400 A are reported. This is made possible for the first time in part due to the recent availability of improved quality bulk GaN substrates.