Demonstration of enhanced continuous-wave operation of blue laser diodes on a semipolar 202¯1¯ GaN substrate using indium-tin-oxide/thin-p-GaN cladding layers

Abstract

The benefits of utilizing transparent conductive oxide on top of a thin p-GaN layer for continuous-wave (CW) operation of blue laser diodes (LDs) were investigated. A very low operating voltage of 5.35 V at 10 kA/cm was obtained for LDs with 250 nm thick p-GaN compared to 7.3 V for LDs with conventional 650 nm thick p-GaN. An improved thermal performance was also observed for the thin p-GaN samples resulting in a 40% increase in peak light output power and a 32% decrease in surface temperature. Finally, a tradeoff was demonstrated between low operating voltage and increased optical modal loss in the indium tin oxide (ITO) with thinner p-GaN. LDs lasing at 445 nm with 150 nm thick p-GaN had an excess modal loss while LDs with an optimal 250 nm thick p-GaN resulted in optical output power of 1.1 W per facet without facet coatings and a wall-plug efficiency of 15%.

Room-Temperature Continuous-Wave Electrically Driven Semipolar (202̅1) Blue Laser Diodes Heteroepitaxially Grown on a Sapphire Substrate

“…AlGaN-cladding free blue LDs were grown on top of the chemo-mechanically polished GaN template. AlGaN-cladding free blue LDs structure was employed and grown by MOCVD, , which comprises a 2.5 μm thick Si-doped n-type GaN (3 × 10 18 cm –3 ), a 60 nm thick In 0.05 Ga 0.95 N waveguide (WG), double InGaN/GaN (3 nm/6 nm) multiple quantum wells (MQWs), a 15 nm thick Mg-doped p-type AlGaN electron blocking layer, a 60 nm thick In 0.05 Ga 0.95 N WG, a 250 nm thick Mg-doped p-type GaN (3 × 10 19 cm –3 ), and a 20 nm thick highly Mg-doped p+GaN (∼2 × 10 20 cm –3 ) for good ohmic contact. The thin p-GaN cladding employed here has been previously proposed and demonstrated to enhance the voltage and thermal performance …”

“…21 AlGaN-cladding free blue LDs were grown on top of the chemo-mechanically polished GaN template. AlGaN-cladding free blue LDs structure was employed and grown by MOCVD, 22,23 which comprises a 2. for good ohmic contact. The thin p-GaN cladding employed here has been previously proposed and demonstrated to enhance the voltage and thermal performance.…”

A tutorial on laser-based lighting and visible light communications: device and technology [Invited]

“…For example, a pulsed high-power AlGaN-cladding-free blue LDs with an optical power of 2.15 W and external quantum efficiency (EQE) of 39% was reported [57]. The InGaN-based LD design and device performance are summarized in Table 2 [1, [58][59][60][61][62][63][64][65][66][67].…”

“…Moreover, by incorporating transparent conducting oxide (TCO) top cladding layers into III-nitride LDs, the device performance can be improved by reducing the growth time and temperature of the p-type layers. Both indium-tin-oxide and zinc oxide (ZnO) have been utilized as the top cladding layer, replacing a thick p-GaN layer to fabricate semipolar GaN LDs [61,63,65]. The improved thermal performance was also observed for the thin p-GaN LDs resulting in a 40% increase in peak light output power and a 32% decrease in surface temperature [61].…”

“…Both indium-tin-oxide and zinc oxide (ZnO) have been utilized as the top cladding layer, replacing a thick p-GaN layer to fabricate semipolar GaN LDs [61,63,65]. The improved thermal performance was also observed for the thin p-GaN LDs resulting in a 40% increase in peak light output power and a 32% decrease in surface temperature [61]. The waveguide design and optimization are other important design factors that have been studied [72][73][74][75].…”