Study on (110)-QW Lasers with Low Threshold Current Density

研究了同一晶片上沿[001]和[110]两个方向排列的宽条(110)-量子阱激光器的阈值电流密度。由于激光沿[001]方向不存在解理面，采用BBr3气体反应离子刻蚀(RIE)形成平行于(001)面的镜面。发现沿[001]方向取向的激光器的阈值电流密度远小于沿[110]方向取向的激光器的阈值电流密度。J<th>中的这种强各向异性被认为来自于[001]方向腔中较强的振子强度，如果表面发射激光器(SELS)采用(110)QW结构，它将非常有助于控制表面发射激光器(SELS)输出激光的偏振。尽管刻蚀后的镜面反射率较低，但沿[001]方向具有腔体的激光器获得了较低的阈值电流密度，小于0.6kA/cm2。随着干法刻蚀(001)面镜反射率的提高，(110)取向的GaInAs(P)量子阱激光器的阈值电流密度将得到较低的阈值电流密度。研究结果表明，沿[001]腔方向的(110)激光器具有预期的优势，表明(110)量子阱结构在长波长面发射激光器的应用中具有优势。由于长波长垂直腔面发射激光器需要更大的光增益来补偿其低的腔镜反射率和对发射光的偏振控制，因此这一研究可能对长波长垂直腔面发射激光器的发展非常有用。

Threshold current densities of (110)-QW lasers were investigated for wide stripes aligned in the [001] and [110] directions from the same wafer. As there is no cleaved facets for lasers along [001] direction, the mirror facets were formed parallel to the (001) face by reactive-ion-etching (RIE) using BBr_3gas. The threshold current densities of the lasers aligned in the [001] direction are found to be much smaller than those aligned in the [110] direction. This strong anisotropy in J_<th> is believed to come from the stronger oscillator strength in the [001] direction cavity and will be very useful to control polrization of laser output from surface emitting lasers (SELs) if the (110) QW structure is used for the SELs. Fairly low threshold current densities of less than 0.6 KA/cm2 were obtained for the lasers with cavities along [001] direction in spite of the lower reflectivity of the RIE-etched mirror surface. With improved mirror reflectivity of the dry-etched (001) face, lower threshold current density will be obtained for the (110)-oriented GaInAs (P) QW lasers.The results in this research show the expected advantage of the (110) lasers along [001] cavity direction and suggests an advantage of the (110) QW structure in the application for long wavelength surface emitting lasers. This research might be very useful for the development of long wavelength vertical cavity surface emitting lasers, as the lasers need more optical gain to compensate their low reflectance of the cavity mirrors and polarization control of the emitting light.