Formation of Sb-Doped SnO[sub 2] p-Type Ohmic Contact for Near-UV GaN-Based LEDs by a CIO Interlayer

Abstract

A Cu-doped In 2 O 3 ͑CIO͒ interlayer was introduced to enhance the electrical and optical properties of Sb-doped SnO 2 ͑ATO͒ p-type electrodes grown by pulsed laser deposition. CIO ͑2.5 nm͒/ATO ͑250 nm͒ contacts become ohmic with specific contact resistance of 2.1 ϫ 10 −3 ⍀ cm 2 and give transmittance of ϳ81% at 400 nm, when annealed at 630°C for 1 min in air. Near-UV ͑400 nm͒ GaN-based light-emitting diodes ͑LEDs͒ fabricated with the CIO/ATO p-electrodes give forward-bias voltage of 3.91 V at injection current of 20 mA and show much higher output power compared to LEDs with conventional Ni/Au p-electrodes.High-brightness GaN-based light-emitting diodes ͑LEDs͒ are of potential importance for solid-state lighting application. For this purpose, the improvement of the luminous efficiency of LEDs is a key factor to be achieved. 1 To increase the luminous efficiency, lowresistance and highly transparent ohmic contacts to p-type GaN should be developed. 1-3 Transparent conducting oxides ͑TCOs͒ have been regarded as potential p-type electrodes, because of their good transparency and moderate resistance. 4,5 Among various TCOs, indium tin oxide ͑ITO͒ is known to be a good p-contact candidate ͑or a p-type current spreading layer͒ for GaN-based LEDs because it has good conductivity and high-transmittance. Indeed, it was shown that ITO-based contacts could serve as promising p-type electrodes for high-performance GaN-based LEDs. 2,6,7 However, ITO has some drawbacks, such as thermal instability and the exhaustion of indium. 4,[8][9][10] Impurity ͑Sb or F͒-doped tin oxide ͑SnO 2 ͒ is an n-type semiconductor having a wide bandgap of 3.6 eV and it has been considered as promising TCOs, 11 which may replace ITO, because of its high thermal and chemical stability. Thus, Sb-or F-doped SnO 2 was used in photovoltaic cells and transparent electrodes. 12 Our group 4 also investigated the electrical and optical properties of pulsed-laserdeposited ͑PLD͒ Sb-doped SnO 2 films ͑ATO͒ and showed that their electrical and optical properties sensitively depend on the oxygen partial pressure. LEDs fabricated with the ATO contacts produced reasonably good performance. In this work, we have attempted to further improve the electrical and optical properties of ATO-based p-type contacts by introducing Cu-doped indium oxide ͑CIO͒ thin layers. It was shown that the CIO/ATO p-contacts give good electrical behaviors when annealed at 630°C in air. Near-UV ͑400 nm͒ LEDs with the CIO/ATO p-contacts produce much better output power compared to those with conventional Ni/Au contacts.1.0 m thick Mg-doped GaN layers ͑with a carrier concentration of 4 ϫ 10 17 cm −3 ͒ were grown using a metallorganic chemical vapor deposition system. The samples were then ultrasonically degreased using trichloroethylene, acetone, methanol, and deionized ͑DI͒ water for 5 min in each step, followed by N 2 blowing. Prior to photolithography, the samples were treated with a buffered oxide etch ͑BOE͒ solution for 20 min and rinsed in DI water. 13 Circular transfer length method ͑C...

Electrical characteristics of Cu-doped In2O3/Sb-doped SnO2 ohmic contacts for high-performance GaN-based light-emitting diodes

“…The STEM, HRTEM, and FFT results imply that annealing causes some amount of Ga atoms to outdiffuse into the interface region. The STEM/EDX results are in good agreement with the Auger electron spectroscopy (AES) data [15].…”

“…First, the improvement is attributed to the fact that the as-deposited amorphous ATO and CIO films become conductive after annealing [15]. It is noted that the CIO films become conductive with a sheet resistance of~26 Ω/sq upon annealing at 630°C, which is comparable to that (~24 Ω/sq) of a reference ITO film.…”

“…This was followed by the PLD growth of 250-nm-thick Sb-doped SnO 2 (ATO) films. Details about the PLD growth were described elsewhere [15]. Some of the samples were annealed at 530 and 630°C for 1 min in air.…”

“…Moreover, PLD generates highly energetic particles, allowing good film quality and good adhesion to substrate [13,14]. Recently, Hong et al [15], investigating PLD Sb-doped SnO 2 (ATO) ohmic contacts to p-GaN, showed that LEDs fabricated with ATO (250 nm thick) combined with a Cu-doped In 2 O 3 (CIO)(2.5 nm thick) interlayer produced much higher output power compared to LEDs with conventional Ni/Au contacts. However, ohmic formation mechanisms for the CIO/ATO p-contacts have not been clearly demonstrated so far.…”

Growth of AlN Thin Film on Sapphire Substrates and ZnO Templates by RF-magnetron Sputtering

“…Solid-state lighting industry is growing bigger and bigger now in general illumination field thanks to high-end white LED devices based on GaN growth technology. Main technology interest in LED industry is fabricating high performance LEDs at low cost and supplying high brightness LEDs at low price in order to penetrate into conservative general illumination industry [1][2][3]. GaN-related nitride semiconductors are typically grown on cheap sapphire substrates, which are thermally and electrically nonconductors, because GaN substrates are very expensive [4,5].…”