GaN Semiconductor Ohmic Contact via Semi-Polar Etching
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Solution Overview
Problem
The challenge lies in achieving a good ohmic contact on the n-type Group-III nitride semiconductor, particularly on the nitrogen polar plane, where existing electrode materials fail to provide effective ohmicity and heat endurance, leading to difficulties in forming a reliable junction for semiconductor devices.
Innovation Solution
The solution involves forming electrodes on semi-polar planes created by anisotropic chemical etching of the n-type Group-III nitride semiconductor, specifically using Ti, Ni, and Au layers on the semi-polar plane and Cr, Ni, and Au layers on the Ga polar plane, which enhances ohmic properties and reduces contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrodes are formed on the nitrogen polar plane of n-type GaN layer, then electrical contact is established, but the ohmic contact characteristic and heat endurance are insufficient
Solution Approach 1:
The patent changes the crystallographic orientation parameter by forming electrodes on semi-polar planes ({10-11} or {20-21} planes) instead of the conventional polar plane (0001 plane). This parameter change in surface orientation fundamentally alters the electronic structure and surface properties, enabling good ohmic contact characteristics that were not achievable on the nitrogen polar plane.
Solution Approach 2:
The patent employs composite electrode structures with multiple material layers (e.g., Ti/Al/Au, Ti/Pt/Au, or Ti/Al alloy layers) deposited on the semi-polar plane. This composite material approach combines the advantages of different materials to achieve both low contact resistance and high heat endurance, resolving the reliability issue.
2Productivity
If sapphire substrate is removed and n-side electrode is formed on the back side of n-type GaN layer, then luminescence efficiency is improved, but good ohmic contact cannot be achieved on the nitrogen polar plane
Solution Approach 1:
The patent changes the crystallographic orientation from the conventional (0001) polar plane to semi-polar planes ({10-11} or {20-21} planes) on the back side of the n-type GaN layer. This parameter change enables the formation of good ohmic contacts while maintaining the substrate-removed structure for high luminescence efficiency.
Solution Approach 2:
The patent introduces a new dimensional approach by utilizing semi-polar planes that are oriented at intermediate angles between the polar and non-polar planes. This dimensional change in surface orientation provides a new solution space where both high luminescence efficiency and good ohmic contact can coexist.
3Reliability
If Cr or Cr alloy layer with Au and Ti layers is used for n-side electrode, then good ohmic contact is achieved on Ga polar plane, but the structure is complex and manufacturing is difficult
Solution Approach 1:
The patent changes the surface orientation parameter to semi-polar planes, which fundamentally alters the interface properties between the electrode materials and GaN. This parameter change enables simplified electrode structures to achieve good ohmic contact, reducing the need for complex multi-layer configurations.
Solution Approach 2:
The patent applies local quality optimization by selecting specific semi-polar plane orientations ({10-11} or {20-21} planes) that inherently provide better contact properties. This localized optimization at the interface level allows for simpler electrode structures while maintaining reliable ohmic contact.
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 allows for the formation of a good ohmic junction on both principal planes, reducing contact resistance and improving the operational efficiency of semiconductor devices, particularly in light-emitting diodes, by increasing the effective contact area and adherence through surface irregularities.
Implementation Method 1
a surface formed by anisotropic chemical etching of a (000-1) N polar plane of the n-type Group-III nitride semiconductor
Implementation Method 2
one electrode of the plurality of electrodes being formed on a surface constituted by a semi-polar plane on the side of one principal plane in an n-type Group-III nitride semiconductor layer
Implementation Method 3
another electrode of the plurality of electrodes that is connected to the one electrode being formed on the side of the other principal plane in the n-type Group-III nitride semiconductor layer
Data Source
AI summary
The purpose of the present invention is to provide a good ohmic contact for an n-type Group-III nitride semiconductor. An n-type GaN layer and a p-type GaN layer are aequentially formed on a lift-off layer (growth step). A p-side electrode is formed on the top face of the p-type GaN layer. A copper block is formed over the entire area of the top face through a cap metal. Then, the lift-off layer is removed by making a chemical treatment (lift-off step). Then, a laminate structure constituted by the n-type GaN layer, with which the surface of the N polar plane has been exposed, and the p-type GaN layer is subjected to anisotropic wet etching (surface etching step). The N-polar surface after the etching has irregularities constituted by {10-1-1} planes. Then, an n-side electrode is formed on the bottom face of the n-type GaN layer (electrode formation step).