Ammonothermal N-face GaN Growth for Smooth Surfaces
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Solution Overview
Problem
Current technology is limited by the poor surface smoothness of N-polar (N-face) and M-plane GaN surfaces, which hinders the development of high-performance opto-electronic and electronic devices such as LEDs, LDs, HEMTs, and transistors due to rough surface profiles, limiting Mg doping concentrations and causing inversion domains and high gate leakage.
Innovation Solution
The ammonothermal growth method is used to directly grow N-face or M-plane GaN with an off-axis angle less than 10 degrees, allowing for the fabrication of GaN layers with high Mg doping concentrations and smooth surfaces, enabling the growth of additional nitride layers without further processing, and resulting in improved device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If VPE growth techniques (MOCVD/MBE) are used to grow GaN layers on heterogeneous substrates, then device layers can be grown epitaxially with a buffer layer providing a smooth surface, but the buffer layer is limited to Ga-polar surface because N-polar growth results in a rough surface
Solution Approach 1:
The invention changes the growth method from conventional VPE (MOCVD/MBE) to ammonothermal growth, which fundamentally alters the growth parameters and mechanism. This enables N-polar GaN layers to be grown with smooth surfaces by controlling temperature, pressure, and ammonia concentration in the supercritical state, overcoming the polarity limitation of VPE techniques
Solution Approach 2:
The invention utilizes the phase transition of ammonia to a supercritical state (above 132°C and 114 atm) as the growth medium. This supercritical ammonia environment enables unique dissolution and precipitation mechanisms that allow N-polar GaN to grow with smooth surfaces, unlike conventional vapor phase methods
2Reliability
If Mg doping concentration is increased in Ga-polar GaN films to improve p-type conduction, then hole concentration increases, but inversion domains form that deteriorate surface smoothness and limit further doping
Solution Approach 1:
Instead of growing Ga-polar films and accepting inversion domain formation, the invention inverts the approach by directly growing N-polar GaN films. This reversal of polarity prevents inversion domain formation entirely, as the growth polarity matches the film polarity, allowing high Mg doping without surface degradation
Solution Approach 2:
The ammonothermal growth method changes the fundamental growth parameters including temperature (500-700°C), pressure (100-300 atm), and ammonia concentration, creating conditions where N-polar growth produces smooth surfaces even with high Mg doping concentrations, eliminating the surface smoothness limitation
3Ease of manufacture
If GaN devices are grown on Ga-polar surface to maintain surface smoothness, then fabrication is straightforward, but gate leakage is high and enhancement-mode operation is difficult to achieve
Solution Approach 1:
The invention changes the substrate polarity from Ga-polar to N-polar through ammonothermal growth, which fundamentally alters the polarization characteristics. This parameter change enables enhancement-mode HEMT operation and reduces gate leakage by reversing the polarization direction, while the supercritical ammonia growth maintains surface smoothness
4Reliability
If N-polar or M-plane GaN surfaces are used to achieve higher Mg doping and improved device performance, then p-type conduction and carrier confinement improve, but surface roughness increases requiring additional processing steps
Solution Approach 1:
The invention uses supercritical ammonia phase transition as the growth medium, which enables direct N-polar or M-plane GaN growth with smooth surfaces. This phase-based growth mechanism eliminates the need for additional surface processing steps that would otherwise be required to achieve smooth surfaces on N-polar or M-plane orientations
Solution Approach 2:
The ammonothermal growth process self-regulates to produce smooth surfaces on N-polar or M-plane GaN through the unique properties of supercritical ammonia dissolution and precipitation, without requiring external intervention or additional processing steps to correct surface roughness
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides smoother surfaces for GaN-based devices, enhancing their performance by increasing Mg doping levels, reducing series resistance, and enabling low gate leakage and enhancement-mode operation, thus overcoming the limitations of existing Ga-polar devices.
Implementation Method 1
growing N-face or M-plane GaN with an off-axis angle less than 10 degrees, allowing for the fabrication of GaN layers with high Mg doping concentrations and smooth surfaces, enabling the growth of additional nitride layers without further processing
Implementation Method 2
The ammonothermal growth method is used to directly grow N-face or M-plane GaN with an off-axis angle less than 10 degrees
Data Source
AI summary
A method for growing III-V nitride films having an N-face or M-plane using an ammonothermal growth technique. The method comprises using an autoclave, heating the autoclave, and introducing ammonia into the autoclave to produce smooth N-face or M-plane Gallium Nitride films and bulk GaN.