This invention is directed to optical devices. In particular, the invention provides a method of manufacture and a device for emitting electromagnetic radiation using nonpolar or semipolar gallium containing substrates, such as GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others. More particularly, the invention provides a device using a gallium and nitrogen containing substrate configured on the {20-21} family of planes or an off-cut of the {20-21} family of planes towards the c-plane and/or towards the a-plane. The invention can be applied to optical devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, as well as other devices.
In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb,” has been used for over one hundred years for a variety of applications including lighting and displays. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to a power source. The conventional light bulb can be found commonly in structures, and is used for indoor and outdoor lighting. Unfortunately, drawbacks exist with the conventional Edison light bulb.
The conventional light bulb dissipates more than 90% of the energy supplied as thermal energy. Reliability is also an issue since the bulb routinely fails due to thermal expansion and contraction of the filament element. In addition, light bulbs emit light over a broad spectrum, much of which does not result in useful illumination due to the spectral sensitivity of the human eye. Another disadvantage is that light bulbs emit light in all directions. Thus they are not ideal for applications requiring strong directionality or focus, such as projection displays, optical data storage, or specialized directed lighting.
In 1960, the laser was first demonstrated by Theodore H. Maiman at Hughes Research Laboratories in Malibu. This laser utilized a solid-state flash lamp-pumped synthetic ruby crystal to produce red laser light at 694 nm. By 1964, blue and green laser light was demonstrated by William Bridges at Hughes Aircraft utilizing an Argon ion laser. The Ar-ion laser utilized Argon as the active medium and produced laser light output in the UV, blue, and green wavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ion laser had the benefit of producing highly directional and focusable light, with a narrow spectral output. The wall plug efficiency, however, was less than 1 percent, and the size, weight, and cost of the lasers were undesirable as well.
As laser technology evolved, more efficient lamp pumped solid state laser designs were developed for the red and infrared wavelengths, but these technologies remained a challenge for blue and green and blue lasers. As a result, lamp pumped solid state lasers were developed in the infrared, and the output wavelength was converted to the visible using special crystals with nonlinear optical properties. For example, a green lamp pumped solid state laser had 3 stages: electricity powers lamp, lamp excites gain crystal which lasers at 1064 nm, 1064 nm radiation goes into frequency conversion crystal which converts it to visible 532 nm. The resulting green and blue lasers were sometimes called “lamp pumped solid state lasers with second harmonic generation.” These lasers had a wall plug efficiency of ˜1%, and were more efficient than Ar-ion gas lasers. They were, however, still too inefficient, large, expensive, fragile for broad deployment outside of specialty scientific and medical applications. Additionally, the gain crystal used in the solid state lasers typically had energy storage properties which made the lasers difficult to modulate at high speeds which limited its broader deployment.
High power diode (or semiconductor) lasers improve the efficiency of these visible lasers. These “diode pumped solid state lasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nm diode laser, 808 nm excites gain crystal which lases at 1064 nm, 1064 nm goes into frequency conversion crystal which converts to visible 532 nm. The DPSS laser technology extended the life and improved the wall plug efficiency of the LPSS lasers to 5-10%. Further commercialization followed, notably into more high-end specialty industrial, medical, and scientific applications. The change to diode pumping, however, increased the system cost and required precise temperature controls, leaving the laser with substantial size and power consumption, while not addressing the properties which made the lasers difficult to modulate at high speeds.
As high power laser diodes evolved and new specialty SHG crystals were developed, it became possible to directly convert the output of the infrared diode laser to produce blue and green laser light output. These “directly doubled diode lasers” or SHG diode lasers had 2 stages: electricity powers 1064 nm semiconductor laser, 1064 nm goes into frequency conversion crystal which converts to visible 532 nm green light. These lasers designs are meant to improve the efficiency, cost and size compared to DPSS-SHG lasers, but the specialty diodes and crystals required make this challenging today. Additionally, while the diode-SHG lasers can be directly modulated, they suffer from sensitivity to temperature which limits their application. Thus techniques for improving optical devices are highly desired.