Exciton localization in polar and semipolar (112̅2) In_0.2Ga_0.8N/GaN multiple quantum wells

Abstract

The exciton localization (ELZ) in polar (0001) and semipolar (112̅ 2) In 0.2 Ga N 0.8 multiplequantum-well (MQW) structures has been studied by excitation power density and temperature dependent photoluminescence. The ELZ in the (112̅ 2) MQW was found to be much stronger (ELZ degree σ E ∼ 40 -70 meV) compared to the (0001) MQW (σ E ∼ 5−11 meV) that was attributed to the anisotropic growth on the (112̅ 2) surface. This strong ELZ was found to cause a blue-shift of the (112̅ 2) MQW exciton emission with rising temperature from 200 to 340 K, irrespective of excitation source used. A lower luminescence efficiency of the (112̅ 2) MQW was attributed to their anisotropic growth, and higher concentrations of unintentional impurities and point defects than the (0001) MQW.

Exciton localization in semipolar (112¯2) InGaN multiple quantum wells

“…This typical morphology has been commonly observed on nonpolar and semipolar (Al,In,Ga)N surfaces. 6,21,[24][25][26][27][28] This can be well explained the anisotropic diffusion of group-III atoms on these surfaces. 26,27,29 The sample grown on a CMP template ( Fig.…”

“…280 K. This can be explained via the hopping processes of excitons through the localized states. 2,3,[15][16][17][18]21 When temperature increases from 10 K to T R!BL , weakly localized carriers are thermally activated and they hop towards other strongly localized states resulting in the initial red-shift of emission energy. With increasing temperature from T R!BL to T BL!R , localized carriers at lower energy levels will be strongly thermally activated to higher levels leading to the blue-shift of emission energy.…”

“…The In-content of the samples was estimated using simulations based on x-ray diffraction measurements. 21,24 To avoid the carrier diffusion problem from GaN to InGaN, TD-PL measurements of the samples have been performed using a continuous-wave violet laser diode (E ex ¼ 3.06 eV) with excitation power densities (P ex ) of 2-15 W/cm 2 . The samples were mounted in a closed-cycle cryostat equipped with a Sumitomo (SHI) Cryogenics aircooled compressor.…”

“…16,17 It should be noted that the ELOC intrinsically exists in InGaN alloys, irrespective of growth orientation employed. 2,3,11,[13][14][15][18][19][20][21] Zhang et al 14 have reported that (11 22) QWs exhibit larger localization depths than polar QWs (estimated from TR-PL measurements at 7 K). Recently, by temperature-dependent photoluminescence (TD-PL) measurements, a strong ELOC degree has been found in (11 22) In 0.2 Ga 0.8 N QWs that causes a blue-shift of the QW exciton emission with rising temperature from $200 K to 340 K, irrespective of excitation source used.…”

“…Recently, by temperature-dependent photoluminescence (TD-PL) measurements, a strong ELOC degree has been found in (11 22) In 0.2 Ga 0.8 N QWs that causes a blue-shift of the QW exciton emission with rising temperature from $200 K to 340 K, irrespective of excitation source used. 21 However, so far there has been no systematic study on the ELOC in (11 22) In x Ga 1Àx N QWs with different In-contents using TD-PL. The most likely reason is due to the high-TDD and high basal-plane stacking fault (BSF) density GaN templates grown on low-cost sapphire substrates that hinder the QW growth.…”