Polarization engineering in GaN power transistors

Abstract

This paper reviews novel design of epitaxial structure for GaN power transistors to reduce the on-state resistance and to increase the breakdown voltage. It takes advantages of the fixed charges at the interfaces caused by the material's inherent polarization, and thus it can be called as polarization engineering. Both AlGaN/GaN superlattices and polarizationmatched InAlGaN quaternary alloy effectively reduce the onstate resistance by using them as capping layers over AlGaN/ GaN combined with the recessed-gate structure. These capping layers successfully eliminate the electron depletion which is caused by the balancing of the fixed charges. The series resistance across the interface is fully reduced so that these capping layers enable low on-state resistance. Proposed natural super junction (NSJ) model well explains the fact that the breakdown voltages of AlGaN/GaN hetero-junction field effect transistors (HFETs) are increased by the extension of the gate and drain spacing. The model assumes that the heterojunction can act an insulator since the polarization induced charges are always balanced at the top and the bottom surfaces. Taking advantages of the model, the fabricated multi-channel AlGaN/GaN diode with dual-recessed structure exhibits high breakdown voltage of 9400 V with low on-state resistance of 52 mV cm 2 , which reaches the predicted performance limit of GaN. The presented polarization engineering is very promising for future improvement of the device performances.

GaN-based multi-two-dimensional-electron-gas-channel diodes on sapphire substrates with breakdown voltage of over 3 kV

“…[16][17][18][19][20][21][22] Other than HEMTs, these 2DEG have also been applied to the drift layer of the lateral diodes. [23][24][25][26][27][28][29][30] In such lateral diodes with a 2DEG drift layer, high breakdown voltage was demonstrated by increasing the anode-cathode distance. [25][26][27] Recently, a low specific on-resistance (R on A) of 52 mΩ cm 2 and a high breakdown voltage of 9400 V were reported for the lateral diodes called natural super-junction diodes consisting of three 2DEG channels.…”

“…[23][24][25][26][27][28][29][30] In such lateral diodes with a 2DEG drift layer, high breakdown voltage was demonstrated by increasing the anode-cathode distance. [25][26][27] Recently, a low specific on-resistance (R on A) of 52 mΩ cm 2 and a high breakdown voltage of 9400 V were reported for the lateral diodes called natural super-junction diodes consisting of three 2DEG channels. 27) Further reduction in R on A is expected for multi-2DEG-channel diodes with more 2DEG channels.…”

“…[25][26][27] Recently, a low specific on-resistance (R on A) of 52 mΩ cm 2 and a high breakdown voltage of 9400 V were reported for the lateral diodes called natural super-junction diodes consisting of three 2DEG channels. 27) Further reduction in R on A is expected for multi-2DEG-channel diodes with more 2DEG channels. However, increasing the number of heterojunctions to increase the number of 2DEG channels might degrade the crystalline quality and the reverse characteristics of such diodes.…”

An ultrahigh performance InGaN/GaN visible-light phototransducer based on polarization induced heterointerface barrier and minority carrier localization

“…[7][8][9][10][11][12] The polarization engineering, based on the regulation of a polarization electric field, also opens up a new way for the structural design of devices such as quantum tunnel diodes, multi junction solar cells, power transistors, photodetectors, and so on. [13][14][15][16] In these advances, however, the polarization effects are still used to improve the performance of existing devices, rarely playing a major functional role.…”

GaN transistors on Si for switching and high-frequency applications

“…1) This 2DEG is due to the high electric field induced by the material's unique polarization that would extend the use of GaN as electron devices utilizing the so-called polarization engineering. 2,3) The first commercial products of the GaN transistors were formed on SiC substrates and operated at microwave frequencies as power amplifiers mainly for cellular base stations. 4,5) Although the operating voltage was as low as 50 V for the output power of 100 W at 1 GHz or higher, the successful commercialization with the established reliability suggested that GaN can be applied also to power switching at higher voltages for which a far larger market has been expected.…”