Semipolar InGaN blue laser diodes with a low optical loss and a high material gain obtained by suppression of carrier accumulation in the p-waveguide region

Abstract

We obtained InGaN laser diodes (LDs) with a low optical loss (1.9 ± 0.6 cm −1 ) by utilizing an undoped In 0.07 Ga 0.93 N p-waveguide (p-WG) and a remote p-AlGaN electron blocking layer. This improvement, however, was accompanied by a low injection efficiency (37%) and a poor material gain. Electroluminescence measurements and energy band diagram simulations revealed excessive carrier accumulation in the p-WG region, which was suppressed by introducing an undoped indium-free GaN p-WG. This enabled LDs with a high material gain, a low optical loss (4.6 ± 0.7 cm −1 ), an improved injection efficiency (60%), and a peak light output power of 1.6 W at 1.5 A.

Demonstration of Efficient Semipolar 410 nm Violet Laser Diodes Heteroepitaxially Grown on High-Quality Low-Cost GaN/Sapphire Substrates

“…29 As shown in Figure 7b, a decent value of 2257 cm −1 was extracted, which is comparable to that reported previously for semipolar LDs grown on bulk GaN. 25 Such an unaffected gain coefficient, on the other hand, explains the similar slope efficiencies and power outputs of the LDs on the GaN/sapphire template and the LDs on bulk GaN, even when the threshold current is much higher.…”

“…Polarization measurements were then carried out by tuning the polarizer so the intensity of the light corresponding to the transverse electric (TE) and transverse magnetic (TM) emission can be obtained. 25 Figure 3c shows the TE and TM emission spectra of the LDs operating at a current of 900 mA. The EL intensity of the TE mode is far stronger than that of the TM mode.…”

“…Also, a top view of the structure showing the segmented contacts for the on-wafer modal gain and optical loss measurements is presented in Figure 2c. 25 A far-field picture depicting the lasing of a semipolar 1200 μm × 8 μm LD is shown in Figure 3a, where the stripes arise from interference of the light reflected from the substrates due to the nature of the etched facets. 26 The spectral information before and after lasing was also obtained, as shown in Figure 3b.…”

“…Therefore, there is no significant difference in terms of optical loss or injection efficiency between the semipolar violet LDs grown on the GaN/sapphire template and the semipolar bulk GaN substrate. On the basis of those values, the threshold modalgain for each QW, g th , can also expressed as 25…”

Influence of InGaN waveguide on injection efficiency in III-nitride laser diodes

“…As was mentioned previously, one of the drawbacks of using InGaN waveguides, despite technological issues in growing high indium content thick layers [20,21], is higher carrier accumulation [19,22]. MEHARI et al [22] found that in semipolar InGaN LDs, when a part of GaN waveguide is replaced by InGaN layer, carriers accumulate in WG. The carrier concentration in the order of 10 19 cm -3 was found to decrease η i due to unwanted recombination of carriers.…”