1. Field of the Invention
The present invention relates to a method for fabricating a vertical-cavity surface-emitting laser diode, more particularly to a method for making the laser device with an amorphous GaAs layer, which is around active layers, and an etched cavity for a single fundamental transverse mode emission, deposited in a low temperature.
2. Description of the Prior Art
The vertical-cavity surface-emitting laser diode is a promising device that can be used as an integrated laser light source in an optical communication system and an optical computer, which can process signals in parallel. The competitive researches for creating an applicable structure are now carried out. A single fundamental transverse mode emission is necessarily required to use such vertical-cavity surface-emitting laser diodes in the optical communication fields.
When an index-guided surface-emitting laser diode having an ion-etched cavity, one of the conventional vertical-cavity surface-emitting laser diodes, is fabricated, it is difficult to obtain a desired stable single fundamental transverse mode laser having a diameter of 7 micro-meter or more due to the strong confinement of the optical field with regards to the structure of etched mirror layer and active layer.
On the other hand, it is generally required to etch a cavity layer using a dry etching process in order to fabricate a vertical-cavity surface-emitting laser having a structure of an index-guided type laser. Herein, the exposed surface of the cavity by the etch process has numerous defects acting as a possible cause of leakage and surface recombination currents. Such leakage and surface recombination currents cause the threshold current of the laser operation to be raised.
In order to eliminate such leakage and surface recombination currents at the etched surface, there have been used the methods of depositing a SiN.sub.x layer therein and re-growing or sulfurizing the crystalline compound semiconductor of GaAs.
For example, the conventional structure for controlling the transverse mode requires a method for stabilizing a single transverse mode through an anti-guiding effect obtained by growing the crystalline AlGaAs/GaAs multi-layers, through a chemical deposition, having a higher refractive index than that of a InGaAs/GaAs active layer or a AlAs/GaAs mirror layer and high resistivity resulting from n-i-p-i doping. It has been shown in the paper, "Low threshold buried heterostructure vertical cavity surface emitting laser"--Appl. Phys. Lett. 63(10), 6 Sep. 1993 0003-6951/93/63(10)/1307/3/$6.00 1993 American Institute of Physics". Namely, the method shows that the crystalline n-i-p-i AlGaAs/GaAs multi-layers have a higher refractive index and a high resistivity are grown around the etched AlAs/GaAs mirror layer and InGaAs/GaAs active layer through the chemical deposition at a high temperature of 600 degrees for the purpose of stabilizing the transverse mode and non-activation of the etched surface.
In the conventional vertical-cavity surface-emitting laser as disclosed in the reference, the device has an advantage of a stabilizing a single transverse mode by the multi-layered structure composed of n-i-p-i AlGaAs/GaAs having a high refractive index.
However, since it has a multi-layered structure, there are problems such as the process steps are increased and the thickness of each layer should be controllably adjusted. In addition, the growth of the crystallized multi-layered structure at the high temperature of 600 degrees makes any associated processes complicated and may cause the thermal damage of device.