Rapid Thermal Processing In Leds
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Some information on the Rapid Thermal Process in LED
Ion implantation doping and isolation coupled with rapid thermal annealing has played a critical role in the realization of high performance photonic and electronic devices in all mature semiconductor material systems. This is also expected to be the case for the binary III-V nitrides (InN, GaN, and A1N) and their alloys as the epitaxial material quality improves and more advanced device structures are fabricated. In "Ion implantation and rapid thermal processing of Ill-V nitrides" reviews the recent developments in implant doping and isolation along with rapid thermal annealing of GaN and the In-containing ternary alloys InGaN and InAlN. In particular, the successful n- and p-type doping of GaN by ion implantation of Si and Mg+P, respectively, and subsequent high temperature rapid thermal anneals in excess of 1000°C is reviewed. In the area of implant isolation, N-implantation has been shown to compensate both n- and p-type GaN, N-, and O-implantation effectively compensates InAlN, and InGaN shows limited compensation with either N- or F-implantation. The effects of rapid thermal annealing on unimplanted material are also presented.
In "Rapid thermal annealed InGaN/GaN flip-chip LEDs",it was stated that Nitride-based flip-chip (FC) light-emitting diodes (LEDs) emitting at 465 nm with Ni transparent ohmic contact layers and Ag reflective mirrors were fabricated. With an incident light wavelength of 465 nm, it was found that transmittance of normalized 300°C rapid thermal annealed (RTA) Ni(2.5 nm) was 93% while normalized reflectance of 300°C RTA Ni(2.5 nm)/Ag(200 nm) was 92%. It was also found that 300°C RTA Ni(2.5 nm) formed good ohmic contact on n+ short-period-superlattice structure with specific contact resistance of 7.8×10-4 Ω·cm2. With 20-mA current injection, it was found that forward voltage and output power were 3.15 V and 16.2 mW for FC LED with 300°C RTA Ni(2.5 nm)/Ag(200 nm). Furthermore, it was found that reliabilities of FC LEDs were good.
Mg-doped GaN films have been successfully prepared on Si(111) substrate by metal-organic chemical vapor deposition (MOCVD). Upon rapid thermal annealing (RTA) treatment, the films showed p-type conductivity with a carrier density of 7.84 cm-3, a mobility of 5.54 cm2V-1s-1, and a resistivity of about 0.144 Ωcm, which were much better than that of the films without rapid thermal annealing (RTA) treatment. It was found that the surface morphology and crystal quality of the obtained p-type GaN films were greatly improved by RTA treatment, while the residual stress and dislocations in these films were decreased.(EFFECT OF RAPID THERMAL ANNEALING ON THE Mg-DOPED GaN/Si FILM).
Etch-induced damage in GaN/InGaN multi-quantum well light-emitting diodes (LEDs) caused by a Cl2-base plasma and its recovery by means of a N2-plasma and annealing process of n-GaN is described. The photoluminescence intensity of etched n-type GaN was decreased by several orders of magnitude due to etch-induced damage, giving rise to an increase in the leakage current in LED current-voltage curves. However, treatment of the LEDs with a N2 plasma along with a rapid thermal annealing process led to an enhancement in the I-V characteristics of the LEDs due to the suppression of the leakage current. The electroluminescence intensity of LEDs which was etched at dc bias of −200 V was also improved by a factor of two relative to the as-etched LEDs, as a result of this treatment(Dry-etch damage and its recovery in InGaN/GaN multi-quantum-well light-emitting diodes)
The maskless selective wet etching of p-GaN layer with KOH in ethylene glycol (KE) and H3PO4/H2SO4 (HH) acids was developed for the highly efficient light-emitting diodes (LEDs). The p-GaN surfaces textured by the selective wet etching process without using etch mask showed hexagonal and stripe shapes in the KE and HH solutions, respectively. The current-voltage (I-V) characteristics of the LED textured by KE and HH solutions showed improved electrical properties compared to the non-etched LED. This result could be attributed to a reduced contact resistance due to an increased contact area between the metal electrode and p-GaN layer. In addition, the light-output power of the LED textured by KE and HH solutions was improved by 29.4% and 36.8% relative to that of the non-etched LED. This result was attributed to the increase in probability of escaping photons from the LED and the reduction of surface defects by the maskless selective wet etching process(Surface texturing of p-GaN layer for efficient GaN LED by maskless selective etching).
In "Fabrication of GaN-based nanorod light emitting diodes using self-assemble nickel nano-mask and inductively coupled plasma reactive ion etching ",the writers report a novel method to fabricate GaN-based nanorod light emitting diodes (LEDs) with controllable dimension and density using self-assemble nickel (Ni) and Ni/Si3N4 nano-masks and inductively coupled plasma reactive ion etching (ICP-RIE). Under the fixed Cl2/Ar flow rate of 50/20 sccm, ICP/Bias power of 400/100 W and chamber pressure of 0.67 Pa, the GaN-based nanorod LEDs were fabricated with density of 2.2 × 109 to 3 × 1010 cm−2 and dimension of 150-60 nm by self assemble Ni nano-masks with various size. The size of Ni/Si3N4 nano-mask was control by the thickness Ni film ranging 150-50 Å and rapid thermal annealing condition. The technique offers a controllable method of fabrication of GaN-based nanorod LEDs and should be applicable for fabrication of the others III-V nanoscale photonic and electronic devices.
To improve the extraction efficiency of InGaN/GaN multiple quantum well light-emitting diodes (LEDs), nanosize cavities were fabricated on a top p-GaN surface by inductively coupled plasma etching utilizing self-assembled platinum clusters as an etch mask. The relative output power was increased up to 88% compared to that of the LED without nanosize cavities. This result could be attributed to an enhancement in the escape of light due to the angular randomization by the nanosize cavities and to the reduced contact resistance due to the increased contact area between the transparent metal layers and the p-GaN(Improvement in Light-Output Power of InGaN/GaN LED by Formation of Nanosize Cavities on p-GaN Surface)
Ni (5 nm)/Au (5 nm) and Ni (5 nm)/indium-tin-oxide (ITO) (60 nm) films were deposited onto glass substrates, p-GaN epitaxial layers and nitride-based light-emitting diode (LED) structures. It was found that the normalized transmittance of subjected to rapid thermal annealing at 300°C Ni/ITO film (300°C-RTA) could reach 90.1% at 460 nm, which was much larger than that of the Ni/Au film. It was also found that the specific contact resistances were 5.0×10-4 Ωcm2, 1.3×10-3 Ωcm2 and 7.2×10-4 Ωcm2 for the Ni/Au, Ni/ITO and 300°C-RTA Ni/ITO contacts on p-GaN, respectively. Nitride-based LEDs with these p-contact layers were also fabricated. It was found that the LED with the 300°C-RTA Ni/ITO p-contact has a reasonably small operation voltage (i.e., 3.29 V at 20 mA). The 20 mA output intensity of the LED with the 300°C-RTA Ni/ITO p-contact is also 65% larger than that of the LED with the Ni/Au p-contact(InGaN/GaN Light-Emitting Diodes with Rapidly Thermal-Annealed Ni/ITO p-Contacts)
The effect of rapid thermal annealing (RTA) on Ni/Au contacts on P-type GaN was investigated in terms of surface morphology and diffusion depth of metallic species. Ni/Au contacts were evaporated on the P-type 0.5 µm thick top layer of a GaN P/N homojunction. Optical micrographs revealed that the contact morphology degrades when annealed above 800°C for 1 min. At the same time, both Ni and Au atoms strongly diffuse in the P-type layer and even can reach the junction for a 1 min long annealing at 900°C, therefore making the junction structure unoperable. This behavior was evidenced using the Auger voltage contrast (AVC) technique(The behavior of Ni/Au contacts under rapid thermal annealing in GaN device structures)